Introduction to R

Lecture 04: Data Visualization with the ggplot2 library

Student Name: Live HTML test

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0.1.0 About Introduction to R

Introduction to R is brought to you by the Centre for the Analysis of Genome Evolution & Function (CAGEF) bioinformatics training initiative. This course was developed based on feedback on the needs and interests of the Department of Cell & Systems Biology and the Department of Ecology and Evolutionary Biology.

The structure of this course is a code-along style; It is 100% hands on! A few hours prior to each lecture, links to the materials will be available for download at QUERCUS. The teaching materials will consist of an R Markdown Notebook with concepts, comments, instructions, and blank coding spaces that you will fill out with R by coding along with the instructor. Other teaching materials include a live-updating HTML version of the notebook, and datasets to import into R - when required. This learning approach will allow you to spend the time coding and not taking notes!

As we go along, there will be some in-class challenge questions for you to solve either individually or in cooperation with your peers. Post lecture assessments will also be available (see syllabus for grading scheme and percentages of the final mark) through DataCamp to help cement and/or extend what you learn each week.

0.1.1 Where is this course headed?

We’ll take a blank slate approach here to R and assume that you pretty much know nothing about programming. From the beginning of this course to the end, we want to take you from some potential scenarios such as…

  • A pile of data (like an excel file or tab-separated file) full of experimental observations that you don’t know what to do with it.

  • Maybe you’re manipulating large tables all in excel, making custom formulas and pivot tables with graphs. Now you have to repeat similar experiments and do the analysis again.

  • You’re generating high-throughput data and there aren’t any bioinformaticians around to help you sort it out.

  • You heard about R and what it could do for your data analysis but don’t know what that means or where to start.

and get you to a point where you can…

  • Format your data correctly for analysis.

  • Produce basic plots and perform exploratory analysis.

  • Make functions and scripts for re-analysing existing or new data sets.

  • Track your experiments in a digital notebook like R Markdown!

0.1.2 How do we get there? Step-by-step.

In the first lesson, we will talk about the basic data structures and objects in R, get cozy with the R Markdown Notebook environment, and learn how to get help when you are stuck because everyone gets stuck - a lot! Then you will learn how to get your data in and out of R, how to tidy our data (data wrangling), and then subset and merge data. After that, we will dig into the data and learn how to make basic plots for both exploratory data analysis and publication. We’ll follow that up with data cleaning and string manipulation; this is really the battleground of coding - getting your data into just the right format where you can analyse it more easily. We’ll then spend a lecture digging into the functions available for the statistical analysis of your data. Lastly, we will learn about control flow and how to write customized functions, which can really save you time and help scale up your analyses.

Don’t forget, the structure of the class is a code-along style: it is fully hands on. At the end of each lecture, the complete notes will be made available in a PDF format through the corresponding Quercus module so you don’t have to spend your attention on taking notes.

0.1.3 What kind of coding style will we learn?

There is no single path correct from A to B - although some paths may be more elegant, or more efficient than others. With that in mind, the emphasis in this lecture series will be on:

  1. Code simplicity - learn helpful functions that allow you to focus on understanding the basic tenets of good data wrangling (reformatting) to facilitate quick exploratory data analysis and visualization.
  2. Code readability - format and comment your code for yourself and others so that even those with minimal experience in R will be able to quickly grasp the overall steps in your code.
  3. Code stability - while the core R code is relatively stable, behaviours of functions can still change with updates. There are well-developed packages we’ll focus on for our analyses. Namely, we’ll become more familiar with the tidyverse series of packages. This resource is well-maintained by a large community of developers. While not always the “fastest” approach, this additional layer can help ensure your code still runs (somewhat) smoothly later down the road.

0.2.0 Class Objectives

This is the fourth in a series of seven lectures. Last lecture we finished up with basic manipulation of data frames with the help of the tidyr package. This week we are taking a break to enjoy the fruits of our labours. Now that we can make properly formatted data frames, we can use these objects as input to produce beautiful, publication-quality data visualizations with the help of the ggplot2 package. This week our topics are broken into:

  1. Introduction to ggplot and the grammar of graphics using scatterplots
  2. Exploring other types of plots
  3. Customizing your plots
  4. Saving your plots
  5. Taking your plots up a notch by combining them and using additional packages.

0.3.0 A legend for text format in R Markdown

  • Grey background: Command-line code, R library and function names. Backticks are also use for in-line code.
  • Italics or Bold italics: Emphasis for important ideas and concepts
  • Bold: Headers and subheaders
  • Blue text: Named or unnamed hyperlinks
  • ... fill in the code here if you are coding along

Blue box: A key concept that is being introduced

Yellow box: Risk or caution

Green boxes: Recommended reads and resources to learn R

Red boxes: A comprehension question which may or may not involve a coding cell. You usually find these at the end of a section.

0.4.0 Lecture and data files used in this course

0.4.1 Weekly Lecture and skeleton files

Each week, new lesson files will appear within your RStudio folders. We are pulling from a GitHub repository using this Repository git-pull link. Simply click on the link and it will take you to the University of Toronto datatools Hub. You will need to use your UTORid credentials to complete the login process. From there you will find each week’s lecture files in the directory /2024-09-IntroR/Lecture_XX. You will find a partially coded skeleton.Rmd file as well as all of the data files necessary to run the week’s lecture.

Alternatively, you can download the R-Markdown Notebook (.Rmd) and data files from the RStudio server to your personal computer if you would like to run independently of the Toronto tools.

0.4.2 Live-coding HTML page

A live lecture version will be available at camok.github.io that will update as the lecture progresses. Be sure to refresh to take a look if you get lost!

0.4.3 Post-lecture PDFs and Recordings

As mentioned above, at the end of each lecture there will be a completed version of the lecture code released as a PDF or HTML file under the Modules section of Quercus.

0.4.4 Microsporidia infection data set description

The following datasets used in this week’s class come from a published manuscript on PLoS Pathogens entitled “High-throughput phenotyping of infection by diverse microsporidia species reveals a wild C. elegans strain with opposing resistance and susceptibility traits” by Mok et al., 2023. These datasets focus on the an analysis of infection in wild isolate strains of the nematode C. elegans by environmental pathogens known as microsporidia. The authors collected embryo counts from individual animals in the population after population-wide infection by microsporidia and we’ll spend our next few classes working with the dataset to learn how to format and manipulate it.

0.4.4.1 Dataset 1: data/infection_signal.tsv

This is an imaging analysis of infected C. elegans strains N2 and JU1400 measuring the overall number of pixels for each animals and the number of fluorescent (infected) pixels within the same area.

0.4.4.2 Dataset 2: data/embryo_data_long_merged.csv

This is a result of our efforts (mostly) from last lecture. After transforming a wide-format version of our measurement data, we merged it with some metadata regarding our experiments and now it is ready to be visualized!

0.4.4.3 Dataset 3: data/infection_meta.csv

We’ll return to this metadata towards the end of lecture but it holds all of the experimental condition information that has been integrated into the embryo_data_long_merged.csv file.

0.5.0 Packages used in this lesson

The following packages are used in this lesson:

  • tidyverse (tidyverse installs several packages for you, like dplyr, readr, readxl, tibble, and ggplot2)

  • RColorBrewer contains a series of different colour palettes

  • viridis contains alternative colour-blind friendly colour palettes

  • ggbeeswarm a package to help visualized grouped datapoints in a sensible way

  • ggthemes a source for alternative plot themes

  • ggpubr used to generate multi-plot figures for publication

  • gridExtra works with ggpubr to produce multi-plot figures

  • ComplexUpset an alternative visualization package to classic Venn diagrams

  • ggrepel used to avoid text overlap (See Appendix)

This week we’ll have a few steps to accomplish installing/working with one of our packages so please follow the instructions carefully.

# Step 1: remove ggplot and reinstall it
remove.packages("ggplot2")
## Removing package from 'C:/Users/mokca/AppData/Local/R/win-library/4.0'
## (as 'lib' is unspecified)
## Error in find.package(pkgs, lib): there is no package called 'ggplot2'
remove.packages("ComplexUpset")
## Removing package from 'C:/Users/mokca/AppData/Local/R/win-library/4.0'
## (as 'lib' is unspecified)
## Error in find.package(pkgs, lib): there is no package called 'ComplexUpset'
# This last line will restart the kernel for you.
.rs.restartR()
## Error in .rs.restartR(): could not find function ".rs.restartR"

If your kernel did not already do so, restart your kernel via the menu at Session > Restart R or using Ctrl + Shift + F10.

# Step 2: after restarting the kernel...
install.packages("ggplot2", repos='http://cran.us.r-project.org')
## Warning: package 'ggplot2' is in use and will not be installed
install.packages("ComplexUpset", type = "source")
## Warning: package 'ComplexUpset' is in use and will not be installed

Proceed with installing the remainder of the packages.

#--------- Install packages to for today's session ----------#
# None of these packages are already available on JupyterHub
install.packages("ggbeeswarm", dependencies = TRUE)
## Warning: package 'ggbeeswarm' is in use and will not be installed
install.packages("ggthemes", dependencies = TRUE)
## Warning: package 'ggthemes' is in use and will not be installed
install.packages("ggpubr", dependencies = TRUE)
## Warning: package 'ggpubr' is in use and will not be installed

0.5.1 You must restart the kernel after initially installing the above packages

#--------- RESTART THE KERNEL BEFORE LOADING PACKAGES! ----------#
#--------- Load packages to for today's session ----------#
library(tidyverse)
library(ggbeeswarm)
library(RColorBrewer)
library(viridis)
library(ggthemes)
library(ggpubr)
library(ComplexUpset)

1.0.0 Introduction to the Grammar of Graphics

One approach to effective data visualization relies on the Grammar of Graphics framework originally proposed by Leland Wilkinson (2005).The idea of grammar can be summarized as follows:

The grammar of graphics is a language to define plotting in a programmatic fashion.

1.1.0 The grammar of graphics with ggplot2

The grammar of graphics facilitates the concise description of any components of any graphics. Hadly Wickham of tidyverse fame has proposed a variant on this concept - the layered grammar of graphics framework. By following a layered approach of defined components, it can be easy to build a visualization. ggplot2 was made to interact well with tidy (long) datasets. If, however, you are spending lots of time figuring out how to make a scatterplot, your data may not be in the correct format.

The Major Components of the Grammar of Graphics by Dipanjan Sarkar

We can break down the above pyramid by the base components, building from the base upwards.

  1. Data: your visualization always starts here. What are the dimensions you want to visualize. What aspect of your data are you trying to convey?

  2. Aesthetics: assign your axes based on the data dimensions you have chosen. Where will the majority of the data fall on your plot? Are there other dimensions (such as categorically encoded groupings) that can be conveyed by aspects like size, shape, colour, fill, etc. This is also known as the mapping layer as we define how variables are mapped to various kinds of output.

  3. Scale: do you need to scale/transform any values to fit your data within a range? This includes layers that map between the data and the aesthetics.

  4. Geometric objects: how will you display your data within your visualization. Which geom_* will you use?

  5. Statistics: are there additional summary statistics that should be included in the visualization? Some examples include central tendency, spread, confidence intervals, standard error, etc.

  6. Facets: will generating subplot of the data add a dimension to our visualization that would otherwise be lost?

  7. Coordinate system: will your visualization follow a classic cartesian, semi-log, polar, etc. coordinate system?

Let’s jump into our first dataset and start building some plots with it shall we?

1.2.0 Build a ggplot layer by layer

Let’s build our first plot step by step to learn more about how ggplot2 works. We will begin by loading datasets from some fluorescence microscopy analysis of C. elegans animals infected by the microsporidia N. ferruginous. This long-format data was measured for total area per animal as well as infected area (ie fluorescent signal) per animal.

Let’s read our first data table. We already loaded the tidyverse package in section 0.5.0 along with a handful of additional packages. You may recall from the startup message that ggplot2 was one of the attached packages.

# Open up the microscopy analysis data
infection_sig.df <- read_tsv("data/infection_signal.tsv")
## Rows: 456 Columns: 14
## -- Column specification ------------------------------------------------------------------------------------------------
## Delimiter: "\t"
## chr (8): exp.name, strain, spore.strain, spore.species, dose, fixing.date, f...
## dbl (6): spores, slide, worm.number, area, percent.infected, area.infected
## 
## i Use `spec()` to retrieve the full column specification for this data.
## i Specify the column types or set `show_col_types = FALSE` to quiet this message.
# Take a look at the data structure
str(infection_sig.df, give.attr = FALSE)
## spc_tbl_ [456 x 14] (S3: spec_tbl_df/tbl_df/tbl/data.frame)
##  $ exp.name        : chr [1:456] "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" ...
##  $ strain          : chr [1:456] "N2" "N2" "N2" "N2" ...
##  $ spore.strain    : chr [1:456] "LUAm1" "LUAm1" "LUAm1" "LUAm1" ...
##  $ spore.species   : chr [1:456] "N.ferruginous" "N.ferruginous" "N.ferruginous" "N.ferruginous" ...
##  $ dose            : chr [1:456] "pulse-72H" "pulse-72H" "pulse-72H" "pulse-72H" ...
##  $ spores          : num [1:456] 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 ...
##  $ fixing.date     : chr [1:456] "rep1" "rep1" "rep1" "rep1" ...
##  $ slide           : num [1:456] 1 1 1 1 1 1 1 1 1 1 ...
##  $ file            : chr [1:456] "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" ...
##  $ worm.number     : num [1:456] 1 2 3 4 5 6 7 8 9 10 ...
##  $ area            : num [1:456] 49838 50425 45533 46459 49215 ...
##  $ percent.infected: num [1:456] 18.53 0 31.16 3.88 0 ...
##  $ area.infected   : num [1:456] 9235 0 14188 1803 0 ...
##  $ timepoint       : chr [1:456] "72hpi" "72hpi" "72hpi" "72hpi" ...

1.2.1 Every ggplot object needs data

We’re going to build this first plot layer by layer and that begins with specifying the data source. In this case, let’s use infection_sig.df to start off our plot. When we see it print, you’ll find that there’s nothing much displayed as output.

# Initialize our ggplot object with some data
# 1. Data
ggplot(data = ...)
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.2 Every ggplot object consists of many parameters

While our above output appears to be just a blank background, we have created a ggplot object. If we were to investigate the structure of this object, we would see it is a list of 9 named elements:

  1. data

  2. layers

  3. scales

  4. guides

  5. mapping

  6. theme

  7. coordinates

  8. facet

  9. plot environment

  10. labels.

Luckily there are some defaults, so we don’t have to specify everything, but you can start to see how ggplot objects are highly customizable. So far, we have only specified the data aspect of this object.

Let’s review the structure of our object first.

# Let's take a quick look at structure of a ggplot object
str(..., give.attr = FALSE)
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.3 aes() determines attributes of the mapping list and how data is displayed

The next step is to choose the data we are plotting (aesthetics) and how it influences the visualization. At this point the data can be scaled directly and the axes appear. We have not yet specified how we want the data plotted, only which data should be plotted. In practice, people usually omit ‘mapping =’, but it is a good reminder that mapping is, in fact, what we are doing.

When we start customizing our plot, our code starts to get a bit harder to read on one line. We can create each specification on a new line by ending each line with a +.

For our plot, we’ll specify the x and y axis using data from the area (total area of the worm imaged in pixels2) and area.infected variables. Note that both of these variables are also numerical in nature, representing a wide range of values. These kinds of values could be considered continuous variables.

# Add the aes() parameter to our plot
ggplot(data = infection_sig.df, mapping = ...)
## Error in eval(expr, envir, enclos): '...' used in an incorrect context
# We can make it equivalent by adding aes() like a layer
# 1. Data
ggplot(infection_sig.df) + 

    # 2. Aesthetics to map the x and y-axis to variables in our data
    ...
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.4 Visualize our data as points on the graph with geom_point()

We now have to choose the geometric object (geom) with which to plot our data, in this case a point. A geom could be a line, a bar, a boxplot - you can type geom_ and then Tab to see all of the available options. Autocomplete can also be helpful for remembering syntax.

Some helpful geom commands:

Command Geom description Used for
geom_point() Single points of data plotted on an x and y axis scatterplots, dotplots, bubble charts
geom_bar() Barchart summarizing data based with heights proportional to size of its group barplots and stacked barplots
geom_col() Barchart summarizing data where with heights representing values in the data barplots of data values?
geom_boxplot() Produce a rough visualization of data distribution boxplots
geom_line() Track values of multiple groups along an x-axis such as time line graphs
geom_jitter() When datapoint overlap too much, you can spread them out using jitter Helpful for boxplots
geom_violin() Combines a kernel distribution estimate in a boxplot-style format Known as the violin plot

For our particular plot, we are making a scatterplot so we’ll want to go with the geom_point() function. Let’s add that layer to the plot with the + syntax.

# Add our data points to the ggplot object
# 1. Data
ggplot(infection_sig.df) + 
    # 2. Aesthetics to map the x and y-axis to variables in our data
    aes(x = area, y = area.infected) +
    # 3. Scaling
    # 4. Geoms
    ... 
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.5 Specify colouring of groups through aes() based on Factors

The data looks like there perhaps may be two groupings with a larger central distribution. My guess would be that there may be different distributions of our points based on worm strain. We can easily test this by colouring our points by the strain variable.

First let’s look at the structure of infection_sig.df in either the Global Environment or using str(). To do this in R, we want to base our colouring on levels from a factor. Afterwards a legend will be automatically created for you.

To accomplish this, we first need to make sure that strain is a column of type Factor. We’ll convert some additional variables to Factor at the same time.

print("Our original infection file")
## [1] "Our original infection file"
str(infection_sig.df, give.attr = FALSE)
## spc_tbl_ [456 x 14] (S3: spec_tbl_df/tbl_df/tbl/data.frame)
##  $ exp.name        : chr [1:456] "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" ...
##  $ strain          : chr [1:456] "N2" "N2" "N2" "N2" ...
##  $ spore.strain    : chr [1:456] "LUAm1" "LUAm1" "LUAm1" "LUAm1" ...
##  $ spore.species   : chr [1:456] "N.ferruginous" "N.ferruginous" "N.ferruginous" "N.ferruginous" ...
##  $ dose            : chr [1:456] "pulse-72H" "pulse-72H" "pulse-72H" "pulse-72H" ...
##  $ spores          : num [1:456] 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 ...
##  $ fixing.date     : chr [1:456] "rep1" "rep1" "rep1" "rep1" ...
##  $ slide           : num [1:456] 1 1 1 1 1 1 1 1 1 1 ...
##  $ file            : chr [1:456] "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" ...
##  $ worm.number     : num [1:456] 1 2 3 4 5 6 7 8 9 10 ...
##  $ area            : num [1:456] 49838 50425 45533 46459 49215 ...
##  $ percent.infected: num [1:456] 18.53 0 31.16 3.88 0 ...
##  $ area.infected   : num [1:456] 9235 0 14188 1803 0 ...
##  $ timepoint       : chr [1:456] "72hpi" "72hpi" "72hpi" "72hpi" ...
# Update our dataframe to convert some variables to factors
infection_sig.df <-
  infection_sig.df %>% 
  # Use the mutate function to replace variables with factor versions of themselves
  ...(strain = ..., 
         spore.strain = factor(spore.strain), 
         spore.species = factor(spore.species),
         fixing.date = factor(fixing.date), 
         dose = factor(dose))
## Error in ...(., strain = ..., spore.strain = factor(spore.strain), spore.species = factor(spore.species), : could not find function "..."
# Take a look at the resulting changes
str(infection_sig.df)
## spc_tbl_ [456 x 14] (S3: spec_tbl_df/tbl_df/tbl/data.frame)
##  $ exp.name        : chr [1:456] "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" ...
##  $ strain          : chr [1:456] "N2" "N2" "N2" "N2" ...
##  $ spore.strain    : chr [1:456] "LUAm1" "LUAm1" "LUAm1" "LUAm1" ...
##  $ spore.species   : chr [1:456] "N.ferruginous" "N.ferruginous" "N.ferruginous" "N.ferruginous" ...
##  $ dose            : chr [1:456] "pulse-72H" "pulse-72H" "pulse-72H" "pulse-72H" ...
##  $ spores          : num [1:456] 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 ...
##  $ fixing.date     : chr [1:456] "rep1" "rep1" "rep1" "rep1" ...
##  $ slide           : num [1:456] 1 1 1 1 1 1 1 1 1 1 ...
##  $ file            : chr [1:456] "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" ...
##  $ worm.number     : num [1:456] 1 2 3 4 5 6 7 8 9 10 ...
##  $ area            : num [1:456] 49838 50425 45533 46459 49215 ...
##  $ percent.infected: num [1:456] 18.53 0 31.16 3.88 0 ...
##  $ area.infected   : num [1:456] 9235 0 14188 1803 0 ...
##  $ timepoint       : chr [1:456] "72hpi" "72hpi" "72hpi" "72hpi" ...
##  - attr(*, "spec")=
##   .. cols(
##   ..   exp.name = col_character(),
##   ..   strain = col_character(),
##   ..   spore.strain = col_character(),
##   ..   spore.species = col_character(),
##   ..   dose = col_character(),
##   ..   spores = col_double(),
##   ..   fixing.date = col_character(),
##   ..   slide = col_double(),
##   ..   file = col_character(),
##   ..   worm.number = col_double(),
##   ..   area = col_double(),
##   ..   percent.infected = col_double(),
##   ..   area.infected = col_double(),
##   ..   timepoint = col_character()
##   .. )
##  - attr(*, "problems")=<externalptr>

How could we have saved ourselves a little trouble by avoiding the mutate command?

Now that we’ve set up some factors within our dataframe, we can begin to use these to help manage some of the information in our visualizations. Note also here that we’ve converted variables of a nature that break our data into distinct groups. These kinds of variables are also known as categorical variables.

1.2.5.1 Set aesthetics parameters within the aes() layer

The aes() layers can be used to set various aspects about our visualization using either continuous or categorical variables. Some of the aesthetics that can be adjusted include:

  • colour: Set the colour of your geom_*() components if applicable like points and lines.
  • fill: Set the fill colour of certain 2-D geom_*() components like points and bars.
  • shape: Set the shape of your geom_*() components like points. This is only suggested for categorical variables.
  • size: Set the size of some geom_*() layers like points - compatible with continuous and categorical variables.

By now you may have noticed that we have been setting specific attributes in an order that matches our diagram of the grammar of graphics pyramid. Keeping this kind of format simplifies the process of tweaking your plots as you first create them.

For our current efforts, let’s map the parameter of colour to our categorical variable strain when we first specify ‘x’ and ‘y’. Before we do that, however, we’ll add a filter() step to our data so that we are only looking at two specific strains - N2 and JU1400.

# Add our data points to the ggplot object
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 
  
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, ...) +
    # 3. Scaling
    # 4. Geoms
    geom_point() 
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.6 Most layers will, by default, inherit from aes() unless explicitly specified

When setting the mapping parameter with aes() there are generally three ways to do this in order of inheritance or precedence

  1. ggplot(data = ... , mapping = (aes(x = ..., y = ..., colour = ...)))

  2. (aes(x = ..., y = ..., colour = ...))

  3. geom_*(aes(x = ..., y = ..., colour = ...))

This means that colour can be specified using geom_point(aes()) since it is a description of the points being plotted. When building a plot, using this command will supersede the plot’s default mappings (if any were created and inherited). By placing version 2 into our code, at the beginning of our plot, we are essentially overriding the default mappings, which are nothing. I prefer to write the code this way for easier reading but method 1 is the more formal way of setting a default mapping to your plot.

It is less common that you might use option (3) but not impossible. Especially when layering multiple geom_*() objects, you may find that you want them coloured in one way, but shaped or sized based on a different factor. Setting the default mappings at the start reduces the effort of adding this information into each new layer of your ggplot object. That’s right, you can have multiple geoms in the same visualization.

#is equivalent in final output to but subsequent layers won't inherit this! compare the consequences

# Add our data points to the ggplot object
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 
  
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected) +
    # 3. Scaling
    # 4. Geoms
    geom_point(...) 
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.7 Altering the scale layer of our axes with scale_y_*()

Some of our data points seem to be compressed along the x-axis. We can see our y-axis ranges from 0 to ~15000. That’s a large range so what might those lower values represent?

Sometimes when we encounter this kind of issue, we can scale the y-axis to get a better look. There are a number of ways to specify how either of the axes of our graph can be scaled. This is usually accomplished through the commands

scale_y_*() and scale_x_*() where * denotes a number of options in R including:

  • discrete
  • continuous
  • log10

Within these commands we can further specify parameters like the the axis name, limits (start and end), breaks (tick mark locations), labels for each break, and transform to alter how the axis is displayed without altering the data. In this case, let’s keep it simple and log-transform our y-axis with scale_y_log10. This will result in stretching out our smaller values a little bit more and compressing our larger values together.

# Convert the y-axis to a log10 scale

# Add our data points to the ggplot object
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 
  
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = strain) +
    # 3. Scaling
    ... +
    # 4. Geoms
    geom_point() 
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

Based on the separation of our points, it looks more now like perhaps our data is also a mixture of measurements from infected animals, some of which may have have been unaffected by the presence of microsporidia. These “unaffected” animals result in area.infected values across the y-axis that are classified as “infinite”. In fact, according to R, these are -inf values.

While these kind of values are still plotted, the warning suggests that we have done something improper.

1.2.8 Alter the scale of axes directly in aes()

Keep in mind that scaling does not change the data, but rather the representation of the data. The y-axis has been scaled. This is different than taking the log10 of the y-axis data.

Can we transform our data directly? Yes, by manipulating the data in our specification of the y-axis data itself in our aes() call but we also need to make a small tweak because, of course, we will run into the same problem because

\[log_{10}(0) = undefined\] but… \[log_{10}(0 + 1) = 0\]

So we can update any 0 values in our data during the time of the log10 transformation. Afterwards take a close look at the resulting y-axis as well!

# Update the y-axis aesthetic to scale the data directly.

# Add our data points to the ggplot object
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 
  
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = ..., colour = strain) +
    # 3. Scaling
    # 4. Geoms
    geom_point() 
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

The placement of the points looks similar, but the first graph is scaling the axis while the second graph has transformed the data values on a log10 scale. Can you see the difference? Take a good look at the name of our y-axis as well!

Don’t be careless with your transformations! While our solution above seemed quite simple, you should proceed with caution when encountering issues like these. Depending on the scale of your values, you may wish pause before deciding to add 1 to your values. You could choose to add smaller values or simply filter your 0 values out. Your choices will depend on your needs.

1.2.8.1 You can assign complex data transformations in aes()

As you can see from above, we performed multiple calculations in our transformation of the area.infected variable. You might have noticed there is also a percent.infected variable in our data as well. However, we can also calculate these values directly in the aes() assignment of the y-axis.

Let’s see how to access those values.

# Calculate percent area infected and compare to just using the supplied variable

# Add our data points to the ggplot object
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 
  
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = ..., colour = strain) +
    # 3. Scaling
    # 4. Geoms
    geom_point()
## Error in eval(expr, envir, enclos): '...' used in an incorrect context
# equivalent to using a pre-calulcated variable
# Use the provided variables of percent.infected
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 
  
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = ..., colour = strain) +
    # 3. Scaling
    # 4. Geoms
    geom_point()
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.9 Take advantage of facet_*() to display multiple conditions in separate panels

What if, instead of colouring our values by strain, we could simply separate them into two different panels?

Faceting allows us to split our data into groups to display in a more separated fashion. This can be helpful when working with multiple overlapping sets of data. By separating data into distinct panels, it can be easier to identify patterns or abnormalities. Note that we have removed the colour specification in our groups as splitting the data into separate graphs accomplishes the same distinction.

There are two facet options to work with:

  1. facet_grid() - this will allow you to facet data by distinct groupings (i.e. factor levels) as columns and/or rows that form grids. This will create plots even where data does not exist for a specified group.

  2. facet_wrap() - this will facet your data based on a specified grouping (also potentially factor levels or distinct values) but will not produce facets (panels) where data does not exist.

Keep things simple: It is good data visualization practice to only have one attribute (colour, shading, faceting, symbols) per grouping. Basically, by choosing carefully, you can represent each attribute of your data across a single visual dimension rather than across multiple ones. This saves on having overly-complicated visualizations and legends.

Let’s facet our data by worm strain using facet_grid() and make use the following parameters throughout the following sections:

  • rows and cols - the set of variables used to group your data across rows and columns. These can also accepts an rowVars ~ colVars formula syntax where rowVars and colVars are grouping variables from your data.

  • scales - used to determine whether x and y axis scales are shared or distinct along individual panels.

  • labeller - takes in a data frame of labels and returns a list or data frame of character vectors. This is helpful for renaming each of your panel titles (aka facet labels).

# Update our aesthetics and add a facet

# Add our data points to the ggplot object
infection_sig.df %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = percent.infected) +
    # 3. Scaling
    # 4. Geoms
    geom_point() +
    # 6. Facets
    ... # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.10 Updating the image size in R Markdown through the code cell definition {r}

You may have noticed that when your legends are quite large, you lose some real estate on your actual graph. This is due to how we output the graphs both when saving and in displaying. In R markdown, the standard output dimension is a 7-inch wide and 5-inch high graph.

When displaying your graphs in R markdown you can update options through the definition of the code cell {r} using the fig.widthand fig.height options to widen or lengthen graphs as you create them with big legends or multiple facets. You’ll need to set this manually for each figure we produce in the notebook. We’ll talk about the process of saving them soon as well. First, let’s fix our previous graph.

# Update our aesthetics and add a facet

# Add our data points to the ggplot object
infection_sig.df %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = percent.infected) +
    # 3. Scaling
    # 4. Geoms
    geom_point() +
    # 6. Facets
    facet_grid(. ~ strain) # use facet_grid to split panels by worm strain

1.2.11 Plots can be coloured using continuous variables

We could now add information from another variable as a colour in this plot. Note that if a variable is continuous instead of discrete, the colour will be a gradient. Let’s switch back to using area.infected for our y-axis and proceed to colour our points by percent.infected. We’ll go back to looking at just the N2 and JU1400 strains from our dataset.

# Update our aesthetics to colour by area.infected

# Add our data points to the ggplot object
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = ...) +
    # 3. Scaling
    # 4. Geoms
    geom_point() +
    # 6. Facets
    facet_grid(. ~ strain) # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.12 Discriminate your variables by shape in the aes() parameters

From our data, there are multiple replicates represented as “repX” within the fixing.date variable. We can explore the consistency of our biological replicates as another dimension in our data by using it to adjust the shape of our points. Let’s associate shape with fixing.date and see if that clarifies anything for us in the visualization. We’ll update the size of our points as well to make things clearer.

Recall that shape can only be used for discrete values.

A quick reference key for shapes can be found in the ‘Cookbook for R’ (http://www.cookbook-r.com/Graphs/Shapes_and_line_types/).

# Revisit the structure of our infection signal dataset
str(infection_sig.df)
## spc_tbl_ [456 x 14] (S3: spec_tbl_df/tbl_df/tbl/data.frame)
##  $ exp.name        : chr [1:456] "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" "N2-LUAm1-1.8" ...
##  $ strain          : chr [1:456] "N2" "N2" "N2" "N2" ...
##  $ spore.strain    : chr [1:456] "LUAm1" "LUAm1" "LUAm1" "LUAm1" ...
##  $ spore.species   : chr [1:456] "N.ferruginous" "N.ferruginous" "N.ferruginous" "N.ferruginous" ...
##  $ dose            : chr [1:456] "pulse-72H" "pulse-72H" "pulse-72H" "pulse-72H" ...
##  $ spores          : num [1:456] 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 ...
##  $ fixing.date     : chr [1:456] "rep1" "rep1" "rep1" "rep1" ...
##  $ slide           : num [1:456] 1 1 1 1 1 1 1 1 1 1 ...
##  $ file            : chr [1:456] "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" "N2.LUAm1.rep1" ...
##  $ worm.number     : num [1:456] 1 2 3 4 5 6 7 8 9 10 ...
##  $ area            : num [1:456] 49838 50425 45533 46459 49215 ...
##  $ percent.infected: num [1:456] 18.53 0 31.16 3.88 0 ...
##  $ area.infected   : num [1:456] 9235 0 14188 1803 0 ...
##  $ timepoint       : chr [1:456] "72hpi" "72hpi" "72hpi" "72hpi" ...
##  - attr(*, "spec")=
##   .. cols(
##   ..   exp.name = col_character(),
##   ..   strain = col_character(),
##   ..   spore.strain = col_character(),
##   ..   spore.species = col_character(),
##   ..   dose = col_character(),
##   ..   spores = col_double(),
##   ..   fixing.date = col_character(),
##   ..   slide = col_double(),
##   ..   file = col_character(),
##   ..   worm.number = col_double(),
##   ..   area = col_double(),
##   ..   percent.infected = col_double(),
##   ..   area.infected = col_double(),
##   ..   timepoint = col_character()
##   .. )
##  - attr(*, "problems")=<externalptr>
# Change our point shape by fixing date and facet by Depth

# Add our data points to the ggplot object
infection_sig.df %>% 
  # Filter the strains we'll investigate
  filter(strain %in% c("N2", "JU1400")) %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected, shape = ...) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5) +
    # 6. Facets
    facet_grid(. ~ strain) # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.13 There are numerous ways to specify facet_*()

Note that up until now we’ve been using facet_grid(~variable) to split our data by variable. This annotation causes the grids to be distributed horizontally. Other ways to facet by a single variable are:

  • facet_grid(variable~.) will distribute your grids vertically

  • facet_wrap(~variable) will return a symmetrical matrix of plots based on levels in your variable.

We can now see that perhaps across both N2 and JU1400, the “rep2” dataset resulted in higher infected area values. This could be a function of specific temperature or doubling time of the spores, or perhaps the total amount of spores used to infect these samples. This is definitely a rep to keep a closer eye on as we may wish to replace this with a more consistent replicate.

One thing that is not necessary in this case - but good to know about - is the ability to allow each grid to have its own independent axis scale. For instance, if the range of our animals varied much more between strains, it might make more sense to allow for separate x and y-axis values between the two data sets. This can be changed, but keep in mind most people will assume all grids have the same scale, so take extra care to point out that the scales are different when presenting or publishing.

# Use facet_wrap to rescale our y-axis individually

# Add our data points to the ggplot object
infection_sig.df %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected, shape = fixing.date) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5) +
    # 6. Facets
    facet_wrap(. ~ strain, scales = ...) # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

1.2.14 facet_grid() and vars() to subgroup by multiple variables from your data

Looking at our above data, there are a few additional ways we could change it. For instance we could alter the colour of our data points to match their fixing.date values. Then we could see the 3 distinct replicate populations on each facet. The other option would be to further dissect out subgroups and organize strains by row and replicates by column.

To accomplish this, we turn to the facet_grid() function and two parameters:

  • cols: the variable you wish to distribute across columns

  • rows: the variable you wish to distribute across rows

To work with these parameters we’ll use the vars() helper function which will evaluate variables or expressions in the context of the accompanying dataset. We can provide vars() with one or more data variable names. In this way, vars() can be used to create subgroups in a manner similar to group_by().

We’ll show two similar examples using facet_wrap() and facet_grid() layers. Note that facet_grid() gives clearer control over how the data is partitioned.

# Use facet_wrap() and vars() to subgroup our data

# Add our data points to the ggplot object
infection_sig.df %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected, shape = fixing.date) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5) +
    # 6. Facets
    facet_wrap(facets = ..., scales = "free_y",
               ncol = 3                    
              ) # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context
# Use facet_grid() and vars() to subgroup our data

# Add our data points to the ggplot object
infection_sig.df %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected, shape = fixing.date) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5) +
    # 6. Facets
    ...(cols = ..., 
               rows = ..., 
               scales = "free_y") # use facet_grid to split panels by worm strain
## Error in ...(cols = ..., rows = ..., scales = "free_y"): could not find function "..."

Notice how facet_grid() produces a much cleaner set of titles and organization for its panels.

1.3.0 Add regression lines using statistical transformations

You can also add statistical transformations to your plots. Again, take a look at stat_ then use Tab to see the list of options. In this case let’s separately fit a linear regression line to area vs area.infected for each facet. The grey area around the line is the confidence interval (default=0.95) and can be removed with the additional call to stat_smooth of se = FALSE.

In our first example, we’ll return the plot to show all data points as the same size.

# Add our regression line with stat_smooth

# Add our data points to the ggplot object
infection_sig.df %>% 
    
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5) +
    # 5. statistics
    ... + ### 1.3.0 add in some regression lines for our data
    # 6. Facets
    facet_wrap(. ~ strain, scales = "free_y") # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context
# Add our regression line with stat_smooth but also group by fixing.date

# Add our data points to the ggplot object
infection_sig.df %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    # 1.3.0-2 use the shape attribute to distinguish reps
    aes(x = area, y = area.infected, colour = percent.infected, shape = ...) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5) +
    # 5. statistics
    stat_smooth(method = lm) + ### 1.3.0 add in some regression lines for our data
    # 6. Facets
    facet_wrap(. ~ strain, scales = "free_y") # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

Notice in our second faceted plot that we have multiple regression lines per panel. This is because by setting the aes(shape = fixing.date) parameter, we have regrouped the data based on fixing.date of which there are 3 factor levels.

1.3.1 Play around with regression models and use the alpha parameter to de-emphasize data

A linear model is not always the best fit. The method of calculating the smoothing function can be changed to other provided functions (such as loess - short for local regression, used below) or can be a custom formula. We’ll talk more about making our own models in Lecture 06! Note that I changed the confidence interval by modifying level=0.8.

geoms_* can also be made more transparent with the alpha parameter, which is set to 0.3 in the following code so that the emphasis is on the regression line rather than the points.

# Set the alpha on geom_point and change our regression method

# Add our data points to the ggplot object
infection_sig.df %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5, alpha = 0.3) +
    # 5. statistics
    stat_smooth(...) + ### 1.3.1 add in some regression lines for our data
    # 6. Facets
    facet_wrap(. ~ strain, scales = "free_y") # use facet_grid to split panels by worm strain
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

Comprehension Question 1.0.0: Now that we’ve built a few basic scatterplots, you may have noticed that our last plot faceted the strains in order of AWR144, AWR145, JU1400, and N2. In fact, we’d like to see a different order of N2 (our lab reference control), JU1400 (a wild isolate), AWR144, and AWR145 (derivatives of JU1400). How would you go about fixing the order? Use the coding cell provided to update the visualization.

# comprehension answer code 1.0.0
# Change the order of how our faceted graph is displayed

# Add our data points to the ggplot object
infection_sig.df %>% 
... %>% 

  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5, alpha = 0.3) +
    # 5. statistics
    stat_smooth(method = loess, level = 0.8) + ### 1.3.1 add in some regression lines for our data
    # 6. Facets
    facet_wrap(. ~ strain, scales = "free_y") # use facet_grid to split panels by worm strain

2.0.0 Exploring different types of distribution plots

Now that we have some of the basics, it’s time to take a closer look at using other types of plots. In this section we’ll focus on distributive plots which can help us visualize the spread or distribution of data in various ways such as with:

We’ll begin by reviewing the embryo_data_long_merged.csv dataset after loading it into memory as the variable embryo_long.df.

We’ll use the col_types parameter to let us define the variable types of the data as we import it.

# Load the tidyverse package
# library(tidyverse)

embryo_long.df <- read_csv("...",
                           # Here we are explicitly specifying our column types
                           ... = 'cnfffnnfllnnfnnffff')     
## Error in read_csv("...", ... = "cnfffnnfllnnfnnffff"): unused argument (... = "cnfffnnfllnnfnnffff")
# Take a look at the  metadata structure
str(embryo_long.df, give.attr = FALSE)
## Error in str(embryo_long.df, give.attr = FALSE): object 'embryo_long.df' not found

Specifying column types with read_csv(): In lecture 02 we allowed read_csv() to directly import our files and make an educated guess on what kind of data was held within. Above we have used the col_types argument and set it using a string of characters that denote shorthand representation for the data type each column. We can use c (character), i (integer), d (double), l (logical), f (factor), and much more! Just be sure you know the column types for all columns in your input! Importing our data this way saves us an extra set of mutate() calls later down the road.

2.0.1 Apply complex functions to grouped data with group_modify()

A quick side note before we continue! Last lecture we spent some time playing with the group_by() and summarize() functions to help generate quick data summaries. There are, however, limitations to summarize() and sometimes you might wish to perform more complex analyses.

The group_modify() allows you to apply a function to each group. This should sound very familiar to the idea behind the apply() family of functions. In the case of group_modify(), the parameters we are concerned with are:

  • .data: the grouped tibble that we are providing for analysis.
  • .f: a function that we wish to apply to the group.
  • ...: additional arguments passed on to .f.

Shortcut functions with the purr package: Note that in the following code we’ll use the “~” in a special way as a shortcut syntax to denote that we are making a new function. This is similar to how functions are defined in the apply() family of functions except it allows us to assign the incoming input to the variable “.x” which we can then manipulate as needed. We’ll learn more about making our own functions in Lecture 07.

For our newly-imported dataset, we are interested in retrieving the mean embryo number for each worm strain replicate (ie Infection Date) under the uninfected (ie Mock) treatment condition.

embryo_long.df %>% 
  # Group by experiment
  group_by(experiment) %>% 
  # Just grab mock infection experiments
  filter(doseLevel == "Mock") %>%
  # Grab the mean embryo count for each exp and make that a new column
  mutate(meanEmb = mean(embryos)) %>% 
  # Grab the first entry of each group
  group_modify(...) %>% 
  # Take a peek at the resulting tables
  head(10)
## Error in head(., 10): '...' used in an incorrect context

Each row in our above output now holds an additional variable, meanEmb, which represent the mean number of embryos present in each experimental grouping. In our final output we used our group_modify() step to retrieve just a single row from each experimental subgroup.

2.0.2 Populate values across groups with *_join()

In the world of C. elegans embryo experiments, there are many factors that can influence reproductive outcomes. While we can reduce intra-experimental variation by using the same source of animals, we may experience inter-experimental variation that can change how well populations of nematodes reproduce.

In order to compare our replicate experiments in a meaningful way, we can normalize our data against these baseline values. You might find the need for similar methods when analysing fluorescent microscopy images.

With our Mock-infection (untreated) condition in a tidy little table, we can now normalize our original datasets with the uninfected baseline for each strain in each specific replicate. All it takes is a little select() and *_join() power!

Using the inner_join() we can pass along our meanEmb variable as a new variable for each observation and the value will be based on matching the Infection Date, wormStrain, and expTimepoint variables. We’ll let inner_join() automatically identify these overlapping variables during the merging process.

We’ll save our normalized data into embryo_norm.df.

embryo_norm.df <-
  embryo_long.df %>% 
  # Group by a few specific variables
  group_by(`Infection Date`, wormStrain, expTimepoint) %>% 
  # Just grab mock infection experiments
  filter(doseLevel == "Mock") %>%
  # Grab the mean embryo count for each exp and make that a new column
  mutate(meanEmb = mean(embryos)) %>% 
  # Grab the first entry of each group
  group_modify(~ head(.x, 1L)) %>% 

  ### Now we have equivalently a summary table of the group means    ###
  ### BUT we also have experimental conditions that they represent!  ###

  # Ungroup the data and treat like a normal table
  ungroup() %>% 
  # We only need to select a few columns from our data - enough to properly join to the original data.
  select(`Infection Date`, wormStrain, expTimepoint, meanEmb) %>%

  # Join the data with the original with the normalization information
  inner_join(x = embryo_long.df, y = .) %>% 

  # Create a normalized embryo variable by calculating embryos/meanEmb for each observation!
  mutate(normEmb = ...)
## Error in embryo_long.df %>% group_by(`Infection Date`, wormStrain, expTimepoint) %>% : '...' used in an incorrect context
# Take a look at the resulting dataframe
head(embryo_norm.df)
## Error in head(embryo_norm.df): object 'embryo_norm.df' not found

2.1.0 View the theoretical distribution of your data with KDE plots

Now that we have our data normalized, we can better compare or combine our replicates for analysis. There are so many observations for each replicate in our data, that it would be nice to see the overall spread of our data. This can be accomplished by simply plotting the data points but with a dense dataset, you might see too much overlap or run into issue with more discrete values. Instead, you might want to know the theoretical distribution of your data - ie the frequency of datapoints you are working with. This kind of plot is known as a kernel density estimate (KDE).

Let’s take a closer look at only the uninfected N2 worm strain and compare the distribution of embryos across different infection dates. We’ll set the alpha parameter to 0.3 so we can see various replicates in our plot.

# Build a density plot of your data

embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2", doseLevel == "Mock") %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(...) + 
    # 4. Geoms
    ... 
## Error in filter(., wormStrain == "N2", doseLevel == "Mock"): object 'embryo_norm.df' not found

As we can see from above, even using a lab reference strain, there can be quite a bit of variation in the distribution of embryo production with our distribution peaks ranging from 15-22. It’s a good thing we normalized the data. Let’s take a quick look at that version for comparison.

# Build a density plot of your data

embryo_norm.df %>% 
    # Filter for uninfected N2 observations
    filter(wormStrain == "N2", doseLevel == "Mock") %>% 
    
    # 1. Data
    ggplot(.) +
        # 2. Aesthetics
        aes(x=..., fill=`Infection Date`) + 
        # 4. Geoms
        geom_density(alpha=0.2) 
## Error in filter(., wormStrain == "N2", doseLevel == "Mock"): object 'embryo_norm.df' not found

You can see that the normalized values center closer around 1.0! So despite the absolute mean values that might occur between experiments, the overall distribution of embryos is mostly consistent. This suggests that there are likely some environmental variables that are slightly affecting the overall number of embryos between replicates.

2.1.1 Set the limits of your axes with *lim()

From both versions of our distributions, we can see that one of the replicates dates (200718) produced a portion of N2 animals with 0 embryos suggesting there may have been some problems with the preparation of these animals. In some cases, you might wish to change your x or y-limits on your axes. This can sometimes be helpful if you have a very long left or right tail, or a partially bimodal distribution where you want to focus in on a single distribution.

You can quickly alter the x and y-axis limits with the xlim() and ylim() layers respectively. You simply need to provide 2 parameters - a lower and upper range.

Let’s do the following:

  1. Set upper and lower x-axis boundaries with xlim().

  2. Add a geom_rug() layer so that we can see where each value falls along the distribution.

# Change our x-axis limits and add a geom_rug()
embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2", doseLevel == "Mock") %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=normEmb, fill=`Infection Date`) + 
    # 3. Scaling
    ... +             ### 2.1.1 add x-axis limits
    # 4. Geoms
    geom_density(alpha=0.2) +
    geom_rug()
## Error in filter(., wormStrain == "N2", doseLevel == "Mock"): object 'embryo_norm.df' not found
  # geom_rug adds lines on the desired axis to indicate data points. 
  # Rug plots display individual cases so are best used with smaller datasets.

2.2.0 Histograms can similarly visualize our distribution

Unlike density plots, histograms count the number of observations you have in each ‘bin’ that you specify. So with proper parameters you can recreate a similar shape to your density plots using only the observed data.

Of bins and binwidths: The geom_histogram() function uses a default bin value of 30 units, which means your data will be subdivided into 30 bins along your x-axis. The geom itself is agnostic to your data, its values, or the meaning (units) of those values. This is simply a default behaviour and you should change it yourself. R will even warn you to change your binwidth using the either the bins or binwidth parameters. The former will set the number of bins, the latter the actual width of the bins.

embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2", doseLevel == "Mock") %>% 

  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=normEmb, fill=`Infection Date`) + 
    # 3. Scaling
    xlim(0.1, 2) +             
    # 4. Geoms
    ...   ### 2.2.0 change it up to a histogram geom
## Error in filter(., wormStrain == "N2", doseLevel == "Mock"): object 'embryo_norm.df' not found

2.2.1 Use the position parameter to alter how data is stacked

Instead of having the normEmb information stacked, we may want to see the data side by side. This can be done with the parameter position set to dodge. It’s not extremely helpful to dodge your data this way when you have many groups, but if you have just a 2 or 3, then the dodge will not look too strange. Let’s try the following:

  1. Filter the data to focus on just 3 replicates
  2. Alter the bin width of the histogram.
  3. Dodge our data
  4. Add a y-axis limit with ylim()
  5. Add a geom_rug()
# Update with dodging the data, ylim and geom_rug

embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2", doseLevel == "Mock", `Infection Date` %in% c("200704", "200711", "200718")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=normEmb, fill=`Infection Date`) + 
  
    # 3. Scaling
    xlim(0.1, 2) + 
    ylim(0, 15) +
  
    # 4. Geoms
    ### 2.2.1 change up the histogram parameters
    geom_histogram(binwidth = ..., position = ..., alpha = 0.5) +   
    geom_rug()
## Error in filter(., wormStrain == "N2", doseLevel == "Mock", `Infection Date` %in% : object 'embryo_norm.df' not found

So for a small number of groups, we can use this kind of approach to look at our data if a histogram is your desired visualization. Of the 3 options, however, a KDE certainly seems the clearest right? Be wary, however, of small population sample sizes since larger variations in these can bias your results. There are also a number of additional geom_density() parameters that can affect your final visualization.

2.3.0 Barplots stack our categorical data by proportion

Can we create a bar plot of embryos per infection dose? With geom_bar() and the proper aes() we can fill in colour along the bar to represent specific infection dates.

The default use of geom_bar() is to create a barchart where the height of each bar is the sum of the total number of observations (ie rows in embryos) for a particular group (ie infection dose level). The default argument for this calculation in geom_bar() is stat="count".

Let’s go ahead and make a bar chart to count how many animals N2 we have used in our experiments, categorizing those counts based on the doseLevel variable. We’ll fill the bar colours based on infection dates.

# What happens if we don't specify an "identity" and y-axis value?

embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2") %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, fill=`Infection Date`) + 
    # 4. Geoms
    ...   ### 2.3.0 change it up to a barplot geom
## Error in filter(., wormStrain == "N2"): object 'embryo_norm.df' not found

2.3.1 Show normalized proportion of subgroups with position_fill()

As you can see above, the bar graphs show the total observations for each Infection Date across each doseLevel. If, however, you want to give a sense of overall proportion, you can bring all of the bars up to the same height by setting the position parameter to position_fill().

This is helpful when trying to convey the percentage a subset of data represents within a grouping.

# What happens if we don't specify an "identity" and y-axis value?

embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2") %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, fill=`Infection Date`) + 
  
    # 4. Geoms
    ### 2.3.1 set the position parameter to position_fill()
    geom_bar(...)   
## Error in filter(., wormStrain == "N2"): object 'embryo_norm.df' not found

Normalized proportion vs absolute count: Depending on the nature of your data, you may wish to display your stacked data by absolute count or by proportion. While our stacked barplot in section 2.3.0 clearly relays the size of our groups AND how subgroups such as replicates are distributed, it is a little harder to guage the overall proportion of each replicate in each bar. On the other hand, by producing a normalized stacked barchart, we can now more accurately gauge the proportions of our subgroups BUT we sacrifice any knowledge of group size as a result.

2.3.2 Stack values of a variable within your geom_bar() using the stat parameter

Suppose we wanted to look at how the sum total of embryos was presented across our barcharts - ie how much do the actual observations contribute to total embryo values? In this case we are no longer looking at the number of observations but the actual measurements from those observations.

There are two ways to accomplish this. The first is to use geom_bar() to visualize the sum of values of a variable by using the stat=identity parameter instead but a y variable must be identified. Let’s show how that can be done.

# Make a bar graph based on embryo counts and fill by Infection Date

embryo_norm.df %>% 
  # Filter for N2 observations regardless of infection status
  filter(wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, y = ..., fill=`Infection Date`) + 
  
    # 4. Geoms
    geom_bar(...)   ### 2.3.2 Sum the actual values from the y-axis
## Error in filter(., wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == : object 'embryo_norm.df' not found

2.4.0 Use geom_col() to produce stacked bar charts of values

Both geom_bar() and geom_col() produce similar results but rather than changing the default behaviour of geom_bar(), if you want to produce a stacked barchart based on values, you should use the appropriate tool: geom_col(). The code is the same except we can use the default parameters to get the same behaviour as above.

# Make a bar graph based on embryo counts and fill by Infection Date

embryo_norm.df %>% 
  # Filter for N2 observations regardless of infection status
  filter(wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, y = embryos, fill=`Infection Date`) + 
  
    # 4. Geoms
    ...   ### 2.4.0 Use geom_col() instead to produce the stacked bar chart
## Error in filter(., wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == : object 'embryo_norm.df' not found

So you can see we’ve generated the exact same output but with slightly less code.

2.4.1 Dodge your barplots with the position parameter

As with our histograms from section 2.2.0 we can choose to unstack our bars and display the categories individually. To do so, you can use the position parameter and set it with position_dodge() or position_dodge2(). Using this option will allow us to see each individual group but each will display a little differently.

Let’s start with position_dodge().

# Make a bar graph based on embryo counts and fill by Infection Date

embryo_norm.df %>% 
  # Filter for N2 observations regardless of infection status
  filter(wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 

  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, y = embryos, fill=`Infection Date`) + 
  
    # 4. Geoms
    geom_col(position = ...)   ### 2.4.1 Use position_dodge()
## Error in filter(., wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == : object 'embryo_norm.df' not found

Looking at the Mock category, we can see that the values don’t appear to sum up to anywhere near 10,000! So where did all of our data go? Looking closely at the bar graph now, it looks like we are only displaying the maximum value for each bar/category. While this appears to be the case, each observation within each group is actually being layered upon one another. Unfortunately, you cannot obtain a subgrouped stack of the values in this way.

Using the position_dodge2() option may help to show our data more distinctly. Let’s see if that works.

# Make a bar graph based on embryo counts and fill by Infection Date

embryo_norm.df %>% 
  # Filter for N2 observations regardless of infection status
  filter(wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, y = embryos, fill=`Infection Date`) + 
  
    # 4. Geoms
    geom_col(position = ...)   ### 2.4.1 Use position_dodge2() to properly view our data
## Error in filter(., wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == : object 'embryo_norm.df' not found

We can see from our bar graph now that each observation is graphed as it’s own bar! If we wanted to dodge with stacked bars (ie using position_dodge()), we would need to use an aggregated set of data to combines observations within replicates.

Comprehension Question 2.4.1: How would we re-use our code from above to generate a dodged barplot where each each Infection Date is the stacked value of embryos across each doseLevel?

# comprehension answer code 2.4.1
# Make a dodged bar graph based on total embryo counts and fill by Infection Date across doseLevels

embryo_norm.df %>% 
  # Filter for N2 observations regardless of infection status
  filter(wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  # Group and summarize your data
  ... %>% 
  ... %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, y = totalEmb, fill=`Infection Date`) + 
    # 4. Geoms
    geom_col(position = position_dodge2())

2.4.2 Flip your data to display horizontally with coord_flip()

Our data looks quite squished when displaying the bars vertically. You can have your bars run horizontally instead of vertically by using the coord_flip() layer. For this simplicity in this example, we’ll return to using position_dodge() even though we know it’s not quite a correct visualization of our data.

# Make a bar graph based on embryo counts and fill by Infection Date

embryo_norm.df %>% 
  # Filter for N2 observations regardless of infection status
  filter(wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=doseLevel, y = embryos, fill=`Infection Date`) + 
    theme(legend.title = element_blank()) + # Update the legend by removing the title
  
    # 4. Geoms
    geom_col(position = position_dodge()) + # Use position_dodge()
  
    # 7. Coordinates
    ...                            ### 2.4.2 Add a coord_flip() layer to our plot
## Error in filter(., wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == : object 'embryo_norm.df' not found

2.4.3 Reorder your categorical x-axis with fct_rev()

Looks like our results aren’t quite what we wanted on that coordinate flip. If you would rather the vertical order of our categories start with “Mock” instead, you can use the fct_rev() function from the forcats package.

This is a simple function that does exactly what we think! It will alter the levels in a factor so that they are in reverse order. Recall that our doseLevel variable is also a factor. Reordering these our categorical axis would not be as easy if we had not already converted this variable into a factor!

More ways to order your factors: The forcats package of the tidyverse actually offers a number of functions that can help to reorder your data based on certain expectations. This can be extremely helpful when, for instance, trying to match your legend to coincide with the vertical order of lines on a linegraph. Check out more functions like fct_reorder2() over on the tidyverse website.

Let’s see how fct_rev() can affect our visualization.

# Make a bar graph based on embryo counts and fill by Infection Date

embryo_norm.df %>% 
  # Filter for N2 observations regardless of infection status
  filter(wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    
    ### 2.4.3 Reorder your x-axis factor. This will become the y-axis!
    aes(x=...,                
        y = embryos, fill=`Infection Date`) + 
    theme(legend.title = element_blank()) +   # Update the legend by removing the title
  
    # 4. Geoms
    geom_col(position = position_dodge()) +   # Use position_dodge()

    # 7. Coordinates
    coord_flip()                              # Add a coord_flip() layer to our plot
## Error in filter(., wormStrain == "N2", (sporeStrain == "ERTm5" | doseLevel == : object 'embryo_norm.df' not found

2.5.0 Boxplots provide visual summary statistics of your data

Boxplots are a great way to visualize summary statistics for your data. As a reminder, the thick line in the center of the box is the median. The upper and lower ends of the box are the first and third quartiles (or 25th and 75th percentiles) of your data. The whiskers extend to the largest value no further than 1.5*IQR (inter-quartile range - the distance between the first and third quartiles).

Data beyond these whiskers are considered outliers and plotted as individual points. This is a quick way to see how comparable your samples or variables are.

The dissection of a boxplot’s components shows us how it summarizes data distribution.

We are going to use boxplots to see the distribution of normalized embryos for N2 across different infections. For this analysis, we’ll actually filter our data twice in order to make sure we capture the values we want to show.

# Let's make a basic boxplot with our embryo data
embryo_norm.df %>% 
  # Filter for N2 observations for infection by ERTm5
  filter(wormStrain %in% c("N2"), 
          # This will filter for N2/ERTm5 experiments or N2/untreated
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 

  # Filter again to just get 3 levels of infection
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>%      

  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=..., y = ...) + # Break data up by experiment along the x-axis
    # 4. Geoms
    ...        ### 2.5.0 Switch over to a boxplot geom
## Error in filter(., wormStrain %in% c("N2"), (sporeStrain == "ERTm5" | : object 'embryo_norm.df' not found

2.5.1 Rotate axis text by updating theme() and angle

Oh no! We can immediately see there are some issues with the plot. Text along the x-axis is overlapping and illegible. Let’s fix the text on the x-axis by rotating it 90 degrees. To accomplish this we will use the theme() layer.

# Access the theme of the plot and update the text angle

embryo_norm.df %>% 
  # Filter for N2 observations for infection by ERTm5
  filter(wormStrain %in% c("N2"), 
          # This will filter for N2/ERTm5 experiments or N2/untreated
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 

  # Filter again to just get 3 levels of infection
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>%      

  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=experiment, y = normEmb) + # Break data up by experiment along the x-axis
    theme(...) +  ### 2.5.1 Rotate the x-axis text
  
    # 4. Geoms
    geom_boxplot()        # 2.5.0 Switch over to a boxplot geom
## Error in filter(., wormStrain %in% c("N2"), (sporeStrain == "ERTm5" | : object 'embryo_norm.df' not found

2.5.2 Justify the axis text through theme() and hjust or vjust

We’ve updated the angle of our text but they’re positioned on somewhat of a “centred” alignment. We can justify the labels such that they align with the x-axis. We will set two parameters in our figure:

  • hjust - horizontal justification which ranges from 0 to 1 (0 = left, 1 = right)

  • vjust - vertical justification which also ranges from 0 to 1 (0 = top, 1 = bottom)

In the case of our text, we are using the hjust to move the labels vertically towards the x-axis while the vjust parameter will help to center our text (horizontall) with the x-axis tick marks. If you look in the help menu at element_text() you will see that the justification is carried out before the rotation. While we can specify the parameters of element_text() in any order, this does not change the order of when they are executed in the function.

# Update our plot to push our text to align with the x-axis

embryo_norm.df %>% 
  # Filter for N2 observations for infection by ERTm5
  filter(wormStrain %in% c("N2"), 
          # This will filter for N2/ERTm5 experiments or N2/untreated
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 

  # Filter again to just get 3 levels of infection
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>%      

  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=experiment, y = normEmb) + # Break data up by experiment along the x-axis
    ### 2.5.2 Adjust the horizontal and vertical justification
    theme(axis.text.x = element_text(angle = 90, ...)) +  
  
    # 4. Geoms
    geom_boxplot()        # 2.5.0 Switch over to a boxplot geom
## Error in filter(., wormStrain %in% c("N2"), (sporeStrain == "ERTm5" | : object 'embryo_norm.df' not found

2.5.3 Slice your data to display what you’d like

Up until now, we’ve been doing some simple filtering on our data but you can really slice and subset your data for exactly what you’d like to display. In this case we’ll perform multiple filters to choose 2 specific worm strains, at the 72-hour timepoint and drop a number of infection dates that have incomplete data.

As long as you have a tibble at the end of your wrangling, you can try to plot it!

We’ll also play around with the aesthetic mapping to produce a grouped box plot by designating colour based on doseLevel and we will facet the plots between our 2 selected worms strains.

# Update our plot to push our text to align with the x-axis

embryo_norm.df %>% 
  ### 2.5.3 Filter for infections by LUAm1 over specific dates
  filter(wormStrain %in% c("N2", "JU1400"), 
         expTimepoint == 72,
         # Drop these 3 replicate dates
         ... c("200912", "200915", "190423"),
         (sporeStrain == "LUAm1" | doseLevel == "Mock")) %>% 
  
  # Filter just for Mock or Medium infection
  filter(doseLevel %in% c("Mock", "Medium")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    ### 2.5.3 Plot by infection date and colour by doseLevel
    aes(x=`Infection Date`, y = normEmb, fill=...) + 
    # Adjust the horizontal and vertical justification
    theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.5)) +  

    # 4. Geoms
    geom_boxplot() +        # 2.5.0 Switch over to a boxplot geom

    # 6. Facets
    facet_wrap(~wormStrain) # Facet output by worm strain
## Error: <text>:8:14: unexpected symbol
## 7:          # Drop these 3 replicate dates
## 8:          ... c
##                 ^

We will be using this graph as a base for customization later in the lesson.

2.6.0 Beeswarm Plots show all of your data points

Even though boxplots give us summary statistics on our data, it is useful to be able to see where our individual data points are. We’ve already used geom_rug() to help visualize our data distribution in density plots.

Similarly, for a boxplot we can add the data as a separate layer using geom_point() to place dots on top of our boxplot, or use geom_jitter() to spread our points out a bit. However, a beeswarm plot places data points that are overlapping (ie same value) next to each other instead of on top of each other, so we can get a better picture of the distribution of our data. We’ll start off by looking at the geom_beeswarm() function from the ggbeeswarm package.

We’ll subset our data to just 3 infection dates using N2 versus the ERTm5 spore strain. After generating the ggplot object, we’ll save it into a variable so we can update it later with geom_beeswarm() layer.

Filter out those 0 values! Remember how I just warned your about log transformations? The ggbeeswarm() package has some issues with -inf values so be sure to filter them out before trying to work with this kind of layer!

# Save our boxplot object to a variable
boxplot <-

  embryo_norm.df %>% 
  # Filter for infections by LUAm1 over specific dates
  filter(wormStrain %in% c("N2"), 
         expTimepoint == 72,
         ... %in% c("200704", "200711", "200718"),
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=`Infection Date`, y = normEmb, fill=doseLevel) + # Plot by infection date and colour by doseLevel
  
    ### 2.5.2 Adjust the horizontal and vertical justification
    theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.5)) +  
  
    # 4. Geoms
    geom_boxplot(alpha = 0.3) +        # 2.5.0 Switch over to a boxplot geom
  
    # 6. Facets
    facet_wrap(~wormStrain)
## Error in filter(., wormStrain %in% c("N2"), expTimepoint == 72, ... %in% : object 'embryo_norm.df' not found
# Display the resulting boxplot
boxplot
## function (x, ...) 
## UseMethod("boxplot")
## <bytecode: 0x00000000266b80a0>
## <environment: namespace:graphics>

2.6.1 Store ggplot objects as variables that you can continue to update

As you can see above, an option with ggplot2 is to save your plot into a ggplot object. This works well if you know you are only changing one or two elements of your plot, and you do not want to keep retyping code. What we are going to vary here is how the data points are displayed.

Now, we can simply overlay the points with geom_beeswarm(). Notice that this geom comes from the ggbeeswarm package and is not a part of ggplot2 itself. However, it was built to work with ggplot2 objects!

# Load the ggbeeswarm package
library(ggbeeswarm)

# Add a geom to our saved plot
boxplot + ...
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

Uh oh! What’s happened above here? As you can see, all our data points have been split by Infection Date but not subgrouped by the doseLevel variable. In order to plot our data in the correct subgroups, we’ll need to set the dodge.width parameter. You can think of this conceptually like dodging in our bar graphs.

Let’s set the dodge.width to 0.78 and see how that goes.

# Update the dodge width to help separate our beeswarm plots

# Add a geom to our saved plot
boxplot + geom_beeswarm(...)
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

2.6.2 cex is a common parameter used to adjust plotting properties of text and symbols

As you can see above, the spacing between points is quite even. Is there an way to change this spacing so the points are further apart?

Depending on the function or geom you may often find that the cex parameter can be adjusted to alter some aspect of how a geom or other graphical layer is displayed. In the case of geom_beeswarm() we can increase the spacing between data points to make its distribution a bit clearer.

# Update the cex parameter
boxplot + geom_beeswarm(dodge.width = 0.78, ...) 
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

Now, while it is nice to see all of our data points, it does appear quite crowded. We see problems especially at the lower area of the plot where there are observations with a value of 0. While we can guess at which grouping these belong to, we cannot know with absolulte certainty. For our audience, this is also a less than ideal presentation of these crowded data points.

2.6.3 Reduce overplotting with geom_quasirandom()

If you think you will have many points to display or if you want to avoid adjusting parameters with each new plot, consider using a geom_quasirandom() to give the empirical distribution of the stripplot to avoid overplotting. It is a geom included with the ggbeeswarm package and can simplify the look and creation of your plots. The distribution mirrors that of a KDE plot and the points are plotted within this theoretical space as a layer on top of your boxplot. We’ll include the width parameter to determine how widely each of our distributions are plotted.

# replace geom_beeswarm() with a geom_quasirandom()
boxplot + geom_quasirandom(dodge.width = 0.78, 
                           width = ..., 
                           alpha = ...) # Set the alpha to make overlapping points more visible
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

Other spacing and distribution options are available at https://github.com/eclarke/ggbeeswarm.

3.0.0 Customizing your plots

3.1.0 Adding a title and axis labels

Let’s start off by sprucing up our plot with

  • ggtitle() to add a title to the plot.
  • ylab() to rename and capitalize our variable name.
  • xlab() to remove the “expKey” label from the plot. Note that I remove the x-axis label by using the keyword NULL.
  • guides() to remove the legend from the right-hand side.

We’ll also update the boxplot outlier colour from black to red using the outlier.colour parameter in geom_boxplot().

# Update the various titles on our plot

embryo_norm.df %>% 
  # Filter for N2 observations to include infection by ERTm5 or any Mock infections
  filter(wormStrain %in% c("N2", "JU1400"), 
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>% 
  # We're going to make a new variable here that combines just Infection date, sporeStrain, and doseLevel
  mutate(expKey = paste(`Infection Date`, sporeStrain, doseLevel, sep="_")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=expKey, y = embryos, 
        fill = expKey) + ### 3.0.1 Update the fill colour using the experiment variable
    
    theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.5)) +  

    ### 3.1.0 Update our titles and remove the legend
    ...("Reproductive capability after infection") +
    ...(NULL) +
    ...("Embryos") + 
    ...(fill="none") +

    # 4. Geoms
    geom_boxplot(outlier.colour = "red") + # Specify the colour of outliers
  
    # 6. Facets
    facet_wrap(~wormStrain) # Facet our data by worm strain
## Error in filter(., wormStrain %in% c("N2", "JU1400"), (sporeStrain == : object 'embryo_norm.df' not found

3.1.1 Use the labs() command to control multiple labels

Using individual commands to alter the x-, y-axis titles and the title of your plot can give you control over aspects of each individual element like font, size, and colour. If you want them to all have a uniform aesthetic, you can simply use the labs() command. This layer can include legend titles too!

# Update the various titles on our plot with labs()

embryo_norm.df %>% 
  # Filter for N2 observations to include infection by ERTm5 or any Mock infections
  filter(wormStrain %in% c("N2", "JU1400"), 
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>% 
  # We're going to make a new variable here that combines just Infection date, sporeStrain, and doseLevel
  mutate(expKey = paste(`Infection Date`, sporeStrain, doseLevel, sep="_")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=expKey, y = embryos, 
        fill = expKey) + ### 3.0.1 Update the fill colour using the experiment variable
    
    theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.5)) +  

    # Update our titles and remove the legend
    ### 3.1.1 Use the labs() command to set all of your labels
    ...(title = "Reproductive capability after infection",
         x = NULL,
         y = "Embryos") +
    guides(fill="none") +

    # 4. Geoms
    geom_boxplot(outlier.colour = "red") + # Specify the colour of outliers
  
    # 6. Facets
    facet_wrap(~wormStrain) # Facet our data by worm strain
## Error in filter(., wormStrain %in% c("N2", "JU1400"), (sporeStrain == : object 'embryo_norm.df' not found

3.1.2 Assigning or altering labels on your plot

Looking at our strain labels for each facet, they are noticeably small and not necessarily self-explanatory. Let’s update the strain label values on these titles so they are more informative and update their themes to be more visible. This can be done in a couple of ways.

One way would be to change the values in the dataset using string manipulation. A second way, would be using the labeller() function. I can make a vector of the updated names to replace ‘N2’ and ‘JU1400’. The data is split by worm strain in the facet_grid() and this is where we pass our labels to labeller(), which will output the names on the strip label. At the same time, we’ll increase the font size and bold it as well using the theme() layer.

I am now going to save this plot in a ggplot object, since we are going to use this as our base plot for the next section.

# Make a named character vector for our labels
... <- c(N2 = "N2 lab reference", JU1400 = "JU1400 wild isolate")

# Assign our plot to an object for alteration later on
my_plot <-

  embryo_norm.df %>% 
  # Filter for N2 observations to include infection by ERTm5 or any Mock infections
  filter(wormStrain %in% c("N2", "JU1400"), 
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>% 
  # We're going to make a new variable here that combines just Infection date, sporeStrain, and doseLevel
  mutate(expKey = paste(`Infection Date`, sporeStrain, doseLevel, sep="_")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=expKey, y = embryos, 
        fill = expKey) + ### 3.0.1 Update the fill colour using the experiment variable
    
    theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.5),   
          ### 3.1.2 Update the facet title font
          ... = element_text(face = "bold", size = 12)                            
         ) +  

    # Update our titles and remove the legend
    # Use the labs() command to set all of your labels
    labs(title = "Reproductive capability after infection",
         x = NULL,
         y = "Embryos") +
    guides(fill="none") +

    # 4. Geoms
    geom_boxplot(outlier.colour = "red") + # Specify the colour of outliers
  
    # 6. Facets
    facet_wrap(~wormStrain, labeller = ...) ### 3.1.2 rename the worm strains
## Error in filter(., wormStrain %in% c("N2", "JU1400"), (sporeStrain == : object 'embryo_norm.df' not found
# display our plot
my_plot
## Error in eval(expr, envir, enclos): object 'my_plot' not found

3.2.0 Colour palettes!

A common custom modification is to change colours from ggplot2’s default rainbow palette. There are many reasons to change a colour palette including

  • making it easier on the reader’s eye.
  • making it colour-blind friendly.
  • plots with continuous data should use good colour spectra for accurate representation.

Let’s create our own colour palette for each experiment in our boxplot.

3.2.1 A Note on Colour Palettes

There are 3 main types of colour palettes in the RColorBrewer package: sequential, diverging and qualitative. We’ll take a few moments to explore each to discern its purpose.

3.2.1.1 Use sequential colour palettes to display low to high values

Sequential

  • Implies an order to your data

  • Light to dark implies low values to high values for instance.

  • Think about using these for purposes such as heatmaps when you would like to see a spectrum of distinguishable shades that also suggest some kind of ordinality.

# Load the RColorBrewer library
library(RColorBrewer)

# display the sequential colour palettes
display.brewer.all(type = "seq")

3.2.1.2 Use diverging colour palettes to highlight the middle and extremes of a distribution

Diverging

  • Low and high values are extremes, and the middle values are still important to distinguish

  • Still goes from light to dark, but 3 colours mainly used.

  • This can also be useful for certain heatmaps if middle values also have an important meaning - such as a kind of inflection point between positive and negative values.

A good example is RNAseq expression data where fold-change might be in the positive or negative direction. Values in the middle range suggest little to no change from control samples and help to distinguish from genes with more interesting changes.

# Display the diverging colour palettes
display.brewer.all(type = "div")

3.2.1.3 Use qualitative colour palettes for categorical data

Qualitative

  • There is no quantitative relationship between colours.

  • This is usually used for categorical data to clearly differentiate between unrelated groups.

  • The lack of relationship between colours helps to highlight the distinction between categorical groups.

display.brewer.all(type = "qual")

3.2.2 Add a colour palette to a plot like a layer

Let’s test one of the RColorBrewer palettes out on our data. We’ll add it as a layer to my_plot using scale_fill_brewer() to override the fill mappings defined in the aes() layer of the plot.

my_plot + scale_fill_brewer(palette = "Spectral")
## Error in eval(expr, envir, enclos): object 'my_plot' not found

3.2.2.1 Colour palettes are not vector recycled when plotting in ggplot

Notice the warning we received: “n too large…”? Note that we have 22 different experimental categories along the x-axis but the Spectral palette only has 11 colours. Unlike when we saw vector recycling in previous lectures, this does not occur when supplying a colour palette with the scale_fill_brewer() layer to our plot. In generating our plot, we only colour the first 11 colours in each facet.

3.2.3 RColorBrewer colour palettes can be created with brewer.pal()

Many colour palettes now exist. I’ll showcase a couple that work nicely with ggplot2. These packages also have colour-blind friendly options.

RColorBrewer has options for these 3 types of palettes, which you can see with display.brewer.all(). With a smaller dataset, we could make a call in ggplot directly to scale_fill_brewer(), which just requires choosing one of RColorBrewer’s palettes, such as “Spectral”. However, we have 22 categories and these palettes have 8-12 colours, so we have to get creative.

Using the brewer.pal() function, we can pull different colours from palettes of our choosing. In our case, I have simply taken the 2 qualitative palettes that each have a length of 12, put them into one palette, and made sure the resulting vector of colour values were unique.

We can then pass this combined colour palette to ggplot via a “native” layer, scale_fill_manual().

display.brewer.all()

Looks like we can use the Paired and Set3 palettes since they both have 12 colours that seem distinct enough. There may be some close colours though.

# Generate 2 palettes from the longest ones
palette1 <- brewer.pal(12, "...")
## Error in brewer.pal(12, "..."): ... is not a valid palette name for brewer.pal
palette2 <- brewer.pal(12, "...")
## Error in brewer.pal(12, "..."): ... is not a valid palette name for brewer.pal
# combine into a single palette
custom <- unique(c(palette1, palette2))
## Error in unique(c(palette1, palette2)): object 'palette1' not found
# Do we still have enough colours?
custom
## Error in eval(expr, envir, enclos): object 'custom' not found
length(custom)
## Error in eval(expr, envir, enclos): object 'custom' not found

Looks like we have enough colours to satisfy our needs. Notice that these are coded using a hexadecimal system? Let’s provide this vector as input.

# Update our plot by adding colour
my_plot + ...(values = custom)
## Error in eval(expr, envir, enclos): object 'my_plot' not found

3.2.4 You can always pick your own colours

You can always choose a vector of your own colors using this R color cheatsheet.

Hexadecimal colours: The RGB colour scheme is represented by 3 colour values (Red, Green and Blue) using a colour scale between 0-255 for each. This blending of shades produces the colours we see and can be represented by a Hexadecimal value ranging from 000000 to FFFFFF. Use an RGB colourpicker if you are obsessed with picking your very own colour palette.

If you just want a repeating patterns of colours, you can use the rep() command to help you out too!

# Reminder of how the rep() command works
rep(c(1,2,3,4),  # The pattern to repeat
    4)           # The number of time to repeat it  
##  [1] 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
# Fill the boxplot using a rep() command
my_plot + scale_fill_manual(values=rep(c("...", "cornflowerblue", "grey", "yellow", "orange", "#FF0000"), 4))
## Error in eval(expr, envir, enclos): object 'my_plot' not found

3.2.5 Colour blind accessible palettes can be found in the viridis package

Sometimes you may wish to work with a colour palette that best represents a continuous series of diverging values. In this case you may also want to ensure your colour palette avoids issues for readers that are printing in greyscale or those that may be colour-blind. The viridis package contains some colour-blind accessible palettes that can also help to really differentiate between the extremes of your spectrum.

The viridis package also has some nice color options (https://cran.r-project.org/web/packages/viridis/vignettes/intro-to-viridis.html). While these might all be diverging palettes (qualitative is best for our experiment variable), we will showcase a couple here.

# Load the viridis package
library(viridis)

# Example 1 with viridis
my_plot + ...(discrete = TRUE)
## Error in eval(expr, envir, enclos): object 'my_plot' not found
# Example 2 with viridis (plasma)
my_plot + scale_fill_viridis(discrete = TRUE, option = ...)
## Error in eval(expr, envir, enclos): object 'my_plot' not found

RSkittleBrewer is another option for funky colour palettes. ggsci has a variety of color palettes inspired by different scientific journals as well as television shows (https://cran.r-project.org/web/packages/ggsci/vignettes/ggsci.html).

3.3.0 Theme: attributes unrelated to your data

As mentioned earlier, it is possible to customize every single aspect of a ggplot. Most of this occurs with a call to theme(), which you can think of as modifying everything BUT your data. For example, my axis labels can be modified, but they (hopefully) have something to do with my data. However, changing the size of the text or the font of the labels is unrelated to my data, and the same structure (text font & size) could be carried over to other plots if I saved my own theme.

Things that you can change with theme() include the axis, legend, panels, gridlines, or background.

Each element of a theme inherits from one of:

  • element_text (text elements like font, colour, size, face (bold, italics), alignment),
  • element_line (grid lines, axis lines),
  • element_rect (panels and backgrounds - colour, size, fill),
  • element_blank (assigns nothing, usually when you are trying to get rid of something),
  • element_grob (making a grid grob).

ggplot2 comes with some themes - I suggest starting with the one that is close to what you want, and then modifying from there.

Check out these themes:

  • theme_minimal()
  • theme_classic()
  • theme_bw()
  • theme_void()
  • theme_dark()
  • theme_gray()
  • theme_light()

You can look at the default for each theme simply by typing it into the console.

theme_bw
## function (base_size = 11, base_family = "", base_line_size = base_size/22, 
##     base_rect_size = base_size/22) 
## {
##     theme_grey(base_size = base_size, base_family = base_family, 
##         base_line_size = base_line_size, base_rect_size = base_rect_size) %+replace% 
##         theme(panel.background = element_rect(fill = "white", 
##             colour = NA), panel.border = element_rect(fill = NA, 
##             colour = "grey20"), panel.grid = element_line(colour = "grey92"), 
##             panel.grid.minor = element_line(linewidth = rel(0.5)), 
##             strip.background = element_rect(fill = "grey85", 
##                 colour = "grey20"), complete = TRUE)
## }
## <bytecode: 0x0000000028566b50>
## <environment: namespace:ggplot2>

And this is what theme_bw() practically looks like:

# Alter the theme of my_plot
my_plot + ... 
## Error in eval(expr, envir, enclos): object 'my_plot' not found

3.3.1 Remember that attribute changes are overridden by order of appearance

Notice how that last addition of the theme_bw() layer overrides my previous changes to the plot like x-axis text orientation? When adding theme() layers, the latest layer takes precedence over previous layers. Any conflicts between theme() layers are overridden by the newly added layers.

In our previous example, the angle of the x-axis text is returned from a vertical to a horizontal orientation since the horizontal orientation is specifically set in the theme_bw() layer.

Here is an example of theme_dark(). I am going to override the default x-axis text angle of this theme by modifying it AFTER I call theme_dark().

# Alter my_plot and fix the x-axis
my_plot + 
  theme_dark() + 
  ...(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.5))
## Error in eval(expr, envir, enclos): object 'my_plot' not found
# When building plots from scratch, be sure to place the theme_* above other theme changes

embryo_norm.df %>% 
  # Filter for N2 observations to include infection by ERTm5 or any Mock infections
  filter(wormStrain %in% c("N2", "JU1400"), 
         (sporeStrain == "ERTm5" | doseLevel == "Mock")) %>% 
  filter(doseLevel %in% c("Mock", "Medium", "High")) %>% 
  # We're going to make a new variable here that combines just Infection date, sporeStrain, and doseLevel
  mutate(expKey = paste(`Infection Date`, sporeStrain, doseLevel, sep="_")) %>% 
  
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=expKey, y = embryos, 
        fill = expKey) + # Update the fill colour using the experiment variable
    
    ### 3.3.1 Add the dark theme first!
    ... +
    ### 3.3.1 Then make your additional thematic adjustments
    theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust = 0.5),
          strip.text.x = element_text(face = "bold", size = 12) 
         ) +  

    # Update our titles and remove the legend
    # Use the labs() command to set all of your labels
    labs(title = "Reproductive capability after infection",
         x = NULL,
         y = "Embryos") +
    guides(fill="none") +

    # 4. Geoms
    geom_boxplot(outlier.colour = "red") + # Specify the colour of outliers
  
    # 6. Facets
    facet_wrap(~wormStrain, labeller = labeller(wormStrain = wormStrain_labels)) # rename the worm strains
## Error in filter(., wormStrain %in% c("N2", "JU1400"), (sporeStrain == : object 'embryo_norm.df' not found

3.3.2 More themes are found in the ggthemes package

ggthemes is a package of themes. Some of these themes are based off of graphs seen in print or on websites (the economist, wall street journal, fivethirtyeight) or to match standard tools (excel, google docs).

See more themes: Information about the ggtheme options can be found at the Github homepage.

Here are 2 possible themes.

# Load the ggthemes package
library(ggthemes)

# Add the economist theme to our plot
my_plot + 
  ... + # Do you enjoy blue background panels?
  theme(axis.text.x = element_text(angle=90, hjust=1)) # fix the x-axis
## Error in eval(expr, envir, enclos): object 'my_plot' not found
# An example of replicating the style from "Stata" software
my_plot + 
  ... + # Blue Plot background with white paneling
  theme(axis.text.x = element_text(angle=90, hjust=1))
## Error in eval(expr, envir, enclos): object 'my_plot' not found

3.4.0 Make a customized theme

You can also make your own custom theme as demonstrated here: http://joeystanley.com/blog/custom-themes-in-ggplot2

I am going to show you how to customize a plot, starting from theme_minimal() because I don’t like the grey backgrounds or harsh axis lines.

# Start by using the minimal theme
my_plot + 
  theme_minimal()
## Error in eval(expr, envir, enclos): object 'my_plot' not found

3.4.1 Fix your plot elements with the theme() layer

Depending on the layout of your plot you can institute changes to the theme as you build your plot or afterwards. Just remember, each call to theme() will override any previous calls that conflict, so the order of changes is important. Many arguments to theme() represent major element categories, but there can be arguments that specifically represent sub-categories or sub-elements.

Things I don’t like about this plot and their solutions:

Problem Solution Layer / Command
x-axis labels overlap and are small rotate labels axis.text.x
facet labels are smaller than axis labels change size and face strip.text.x
title is not centered adjust position horizontally plot.title
need a border to separate strains create a border around each panel panel.border
add y axis ticks update y axis ticks axis.ticks.y

Theme layers are like onions: No, not smelly. There are just a lot of them. It isn’t necessary to remember all of this syntax! It’s certainly helpful but you can just bookmark the ggplot2 theme reference page instead.

As mentioned the last call to theme() will override previous calls that conflict. Therefore, if we want to start with theme_minimal() as our base, it has to be in our code BEFORE the other modifications.

# Add our own theme elements
my_plot + 
  theme_minimal() + # start with theme minimal
  theme(axis.text.x = ...(angle = 90, hjust = 1, vjust=0.5, size=14), # Adjust x-axis text and position
        panel.border = ...(fill=NA), # Add a panel border to each facet
        strip.text.x = element_text(face = "bold", size = 16), # alter the facet title text
        plot.title = element_text(hjust=0.5, size = 18), # Centre that plot title
        axis.ticks.y = ...()) # Add some little tick marks on the y-axis
## Error in eval(expr, envir, enclos): object 'my_plot' not found
# Note that you could break this into multiple theme() calls as well!

There are a lot of way to customize your plots! Keep exploring and playing with parameters!

3.4.2 Save your personalized themes to a variable

You may be wondering, “Can I save this awesome theme to apply to all my amazing plots?” Yes, there are a number of ways to import your themes to other scripts if you learn to save your data objects to file in Lecture 07! For now, you can assign your themes to a variable and apply them to plots like any other layer.

Work smarter not harder: A key advantage to saving your theme to a variable is that once you save it, you can apply it easily to all of your plots but you can also update and tweak your theme in a single place within your code or notebook, rather than across multiple code cells, etc.!

# Save you theme to a variable
... <-
  theme_minimal() + # start with theme minimal
  # Our previous theme update
  theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust=0.5, size=14),
        panel.border = element_rect(fill = NA),
        strip.text.x = element_text(face = "bold", size = 16),
        plot.title = element_text(hjust=0.5, size = 18),
        axis.ticks.y = element_line())
# Apply your theme as a layer
my_plot + theme_personal
## Error in eval(expr, envir, enclos): object 'my_plot' not found

Comprehension Question 3.0.0: Alter the my_plot background to a cornflower blue and add major/minor gridlines in black. You can accomplish this by updating the theme() layer. Hint: you can use the plot.background, panel.grid.minor, and panel.grid.major arguments.

# comprehension answer code 3.0.0 - updating the plot background and gridlines
# Fill the blanks
my_plot + 
  theme_minimal() + # start with theme minimal
  # Our previous theme update
  theme(axis.text.x = element_text(angle = 90, hjust = 1, vjust=0.5, size=14),
        panel.border = element_rect(fill = NA),
        strip.text.x = element_text(face = "bold", size = 16),
        plot.title = element_text(hjust=0.5, size = 18),
        axis.ticks.y = element_line()) +

  # Our current theme update
  theme(..., # Set the background to a rectangle with new colour
        ..., # Add minor grid lines
          ...) # Add black major grid lines

4.0.0 Saving your figures

Up until now, we have taken for granted that our plots have been displayed using a Graphic Device. For our Markdown Notebooks we can see the graphs right away and update our code. You can even save them manually from the output display but sometimes you may be producing multiple visualizations based on large data sets. In this case it is preferable to save them directly to file.

4.1.0 Graphics Devices

  • Plots must be created on a graphics device

  • The default graphics device is almost always the screen device, which is most useful for exploratory analysis.

  • File devices are useful for creating plots that can be included in other documents or sent to other people.

  • For file devices, there are vector (pdf, svg, postscript) and bitmap (png, jpeg, tiff) formats.

  • Vector formats are good for line drawings and plots with solid colors using a modest number of points.

  • Bitmap formats are good for plots with a large number of points, natural scenes or web-based plots.

(https://rdpeng.github.io/Biostat776/notes/pdf/grdevices.pdf)

ggplot2 has its own function for saving its graphics: ggsave(). This allows us to skip the step of explicitly calling separate graphics devices and shutting them down afterwards (if you have saved plots in base R or lattice, this will sound familiar to you).

You can send the plot object to the screen device to preview your image, and then save that image by specifying the file device. If you do not specify the device type, ggsave() will guess it from your filename extension (pdf, jpeg, tiff, bmp, svg or png). Note that this will save whatever graphic was last on your screen device.

With ggsave() you can minimally input the filename you would like to have, and the path to your file.

# Save the last plot displayed by ggplot
ggsave("...", path = "data")
## Error in `ggsave()`:
## ! Can't save to data/....
## i Either supply `filename` with a file extension or supply `device`.

However, in some cases you want to tailor your output. You can specify the width, height and units of your image, or you can apply a scaling factor (the ‘eyeballing’ approach). You can also specify the plot object you want to save instead of whatever was on your graphics device last using the ‘plot’ parameter. Note that this time I have combined the path with the filename, and called the file device type separately.

# Save our altered plot to an object
saved_plot <- my_plot + theme_personal
## Error in eval(expr, envir, enclos): object 'my_plot' not found
# Specifically make saved_plot a pdf!
ggsave("data/crazy_blue_graph2.pdf", # The path for our output
       plot = saved_plot, # The object we want to save
       device = "pdf", # explicitly name the type of file we want to make, despite the name
       scale = 2, width = 250, height = 110, units = "...") # Set some parameters for the final size
## Error in `plot_dim()`:
## ! `units` must be one of "in", "cm", "mm", or "px", not "...".

No image is sent to the screen device when a file is saved in this manner.

5.0.0 Taking it up a notch with the ggpub package

There are many fantastic R packages to analyze and visualize your data. As a group, we are likely working in a variety of specialized areas. The plots we have made so far today should be useful for data exploration for many different kinds of data. In the next section we are going to preview some more complex visualization types, but since these take more time to go through and not everyone may be interested in interactive graphics, network diagrams, time-series analysis, or geospatial data, we will not be plotting all of these together. We will, however learn how to arrange multiple plots per page, and also how to make an upset plot.

5.1.0 Multiple plots on one page (ie. for publication images) with ggarrange()

There are a variety of methods to mix multiple graphs on the same page, however ggplot2 does not work well with all of them. I am going to work with a package base called ggpubr which allows us to align the axes of our plots. This package relies on gridExtra (which allows us to arrange plots) and works well with ggplot2.

For a demonstration, we are going to take 3 plots that we made earlier (a beeswarm plot, a KDE plot, and a scatter plot), save them as objects, and then arrange and align them in the same figure. (http://www.sthda.com/english/rpkgs/ggpubr/)

ggarrange() is a function from ggpubr that takes your plots, their labels, and how you would like your plots arranged in rows and columns. It takes the form of:

ggarrange(
  ...,
  plotlist = NULL,
  ncol = NULL,
  nrow = NULL,
  labels = NULL,
  label.x = 0,
  label.y = 1,
  hjust = -0.5,
  vjust = 1.5,
  font.label = list(size = 14, color = "black", face = "bold", family = NULL),
  align = c("none", "h", "v", "hv"),
  widths = 1,
  heights = 1,
  legend = NULL,
  common.legend = FALSE,
  legend.grob = NULL
)

Of the parameters some relevant ones for us are:

  1. ... - the list of plots to be arranged as a grid or alternatively use…

  2. plotlist - An optional list of plots to display

  3. labels - An optional list of labels for each plot

  4. ncol - number of columns in the plot grid (optional)

  5. nrow - number of rows in the plot grid (optional)

Some examples of simple grid arrangements are :

To start, we want our boxplot and dot plot side by side. If you picture each plot as a square in a grid, we need two columns (one for each plot, ncol = 2) and one row (since they are side by side, nrow = 1).

# Load the ggpubr package
library(ggpubr)

# Create a KDE
densityPlot <- 
  embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2", doseLevel == "Mock") %>% 
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=normEmb, fill=`Infection Date`) + 
    # 3. Scaling
    xlim(0.1, 2) +             ### 2.1.1 add x-axis limits
    # 4. Geoms
    geom_density(alpha=0.2) +
    geom_rug()
## Error in filter(., wormStrain == "N2", doseLevel == "Mock"): object 'embryo_norm.df' not found
# Create a scatter plot
scatterPlot <- 
  infection_sig.df %>% 
  filter(strain %in% c("N2", "JU1400")) %>% 
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected) +
    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5, alpha = 0.3) +
    # 5. statistics
    stat_smooth(method = loess, level = 0.8) + ### 1.3.1 add in some regression lines for our data
    # 6. Facets
    facet_wrap(. ~ strain, scales = "free_y") # use facet_grid to split panels by worm strain

# Set up a beeswarm for our example
beeswarmPlot <- 
  boxplot + 
  theme(axis.text.x = element_text(angle=0, hjust=0.5, vjust = 1)) +
  geom_quasirandom(dodge.width = 0.78, width = 0.1, alpha = 0.5)

Now lets arrange the scatter and KDE plots beside each other in a single row. To accomplish that we consider that nrow=1 and ncol=2.

# Arrange the two plots in a single page    
ggarrange(..., ..., # Plots (and their order)
          labels = c("A", "B"),
          ncol = ..., nrow = ...)
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

5.1.1 Move legend elements around through the guides() and theme() layers

While the grid areas are of the same size, the backgrounds are not. Let’s adjust the legend of our histogram so that it is in the top right corner of the plot, and remove the white background. The movement of the legends requires a couple of layer steps to accomplish:

  1. guides() - using this layer will allow us to denote the overall position of any attribute guide (aka legend) we’ve created. There are a few different possible kinds of guides like guide_bins, guide_colourbar, and guide_legend which will be chosen based on your type of data/legend.

  2. themes() - we are already acquainted with this a little, but within this layer we will use the legend.position.inside parameter which uses a tuple (pair of numbers) where each value is {0,1}. (0,0) is the lower-left and (1,1) is the upper-right of a graph. You can also set multiple unassigned legends with the legend.position parameter if they don’t already have a designation in the guides() or other layers. With this paremeter, you can specify “left”, “right”, “top”, and “bottom” for positions outside your graph.

  3. The legend.background parameter and others can be set to elements like a element_rect() but they can also be removed using the placeholder element_blank(). We’ll use this to make the legends backgrounds transparent when placed inside your plot panels.

##----------## Alter our KDE ##----------##
densityPlot <- 
  embryo_norm.df %>% 
  # Filter for uninfected N2 observations
  filter(wormStrain == "N2", doseLevel == "Mock") %>% 
  # 1. Data
  ggplot(.) +
    # 2. Aesthetics
    aes(x=normEmb, fill=`Infection Date`) + 
    ### 5.1.1 Set the anchor position of the legend box.
    theme(legend.justification=...,      
          ### 5.1.1 Reposition the legend based on its anchor to the top right
          legend.position.inside=...,          
          ### 5.1.1 Remove the background of the legend
          legend.background = ...,   
          plot.title = element_text(hjust=0.5, size = 18)) + 
    
    ### 5.1.1 Send the legend to the inside of the plot
    guides(fill = guide_legend(position = ...)) +

    # Add a title and axis labels
    labs(title = "Density plot of N2 normalized embryo counts",
         x = "Normalized embryo count",
         y = "Density") +

    # 3. Scaling
    xlim(0.1, 2) +             # add x-axis limits
    # 4. Geoms
    geom_density(alpha=0.2) +
    geom_rug()
## Error in filter(., wormStrain == "N2", doseLevel == "Mock"): object 'embryo_norm.df' not found
##----------## Alter our scatter plot ##----------##
scatterPlot <- 
  infection_sig.df %>% 
  filter(strain %in% c("N2", "JU1400")) %>% 
  # 1. Data
  ggplot(.) + 
    # 2. Aesthetics
    aes(x = area, y = area.infected, colour = percent.infected) +
    ### 5.1.1 Set the anchor position of the legend box.
    theme(legend.justification=c(1,1),  
          ### 5.1.1 Reposition the legend based on its anchor to the top right
          legend.position.inside=c(1,1),       
          ### 5.1.1 Remove the background of the legend
          legend.background = element_blank(),   
          plot.title = element_text(hjust=0.5, size = 18)) + 

    ### 5.1.1 Send the legend to the inside of the plot
    guides(colour = guide_colourbar(position = "inside")) +
  
    # Add a title and axis labels
    labs(title = "Scatterplot of JU1400 and N2 infection signals",
         x = "Area (px^2)",
         y = "Area infected",
         colour = "% infected") +

    # 3. Scaling
    # 4. Geoms
    geom_point(size = 2.5, alpha = 0.3, ) +
    # 5. statistics
    stat_smooth(method = loess, level = 0.8) + ### 1.3.1 add in some regression lines for our data
    # 6. Facets
    facet_wrap(. ~ strain, scales = "free_y") # use facet_grid to split panels by worm strain

##----------## Alter our beeswarm plot ##----------##
beeswarmPlot <- 
  boxplot + 
  theme(axis.text.x = element_text(angle=0, hjust=0.5, vjust = 1)) +

  ### 5.1.1 Set the anchor position of the legend box.
  theme(legend.justification=c(1,1),    
        ### 5.1.1 Reposition the legend based on its anchor to the top right
        legend.position.inside=c(1,1),                
        ### 5.1.1 Remove the background of the legend
        legend.background = element_blank(),   
        plot.title = element_text(hjust=0.5, size = 18)) + 
  
    ### 5.1.1 Send the legend to the inside of the plot
    guides(fill = guide_legend(position = "inside")) +

  # Add a title and axis labels
  labs(title = "Boxplot and beeswarm of N2 infection by ERTm5",
       x = "Microsporidia dose",
       y = "Normalized embryo count",
       fill = "Dose Level") +

  geom_quasirandom(dodge.width = 0.78, width = 0.1, alpha = 0.5) 
## Error in boxplot + theme(axis.text.x = element_text(angle = 0, hjust = 0.5, : non-numeric argument to binary operator
# Display our updated plots
densityPlot
## Error in eval(expr, envir, enclos): object 'densityPlot' not found
scatterPlot
## `geom_smooth()` using formula = 'y ~ x'
## Warning: The following aesthetics were dropped during statistical transformation: colour.
## i This can happen when ggplot fails to infer the correct grouping structure in the data.
## i Did you forget to specify a `group` aesthetic or to convert a numerical variable into a factor?
## The following aesthetics were dropped during statistical transformation: colour.
## i This can happen when ggplot fails to infer the correct grouping structure in the data.
## i Did you forget to specify a `group` aesthetic or to convert a numerical variable into a factor?

beeswarmPlot
## NULL
# Arrange the plots again
ggarrange(scatterPlot, densityPlot, 
          labels = c("A", "B"),
          ncol = 2, nrow = 1)
## Error in ggarrange(scatterPlot, densityPlot, labels = c("A", "B"), ncol = 2, : object 'densityPlot' not found

5.1.2 Arrange plots within plots

Next we will add in the boxplot by nesting a ggarrange() call within another.

Imagine a square with 4 quadrants.

  1. We are going to put our beeswarm in the left-hand side across the top and bottom quadrants.

  2. The density plot will be placed in the top right quadrant.

  3. The scatter plot goes in the bottom right quadrant.

To do this, we are arranging 2 columns (one with the boxplot and one with the KDE plot + scatterplot, ncol = 2) and we are arranging 2 rows (one with the KDE and one with the scatterplot, nrow = 2).

# Build our new grid setup    
# 1. First call initiates the 2-column grid
ggarrange(..., # The left-hand column is a boxplot
          ...(..., ..., # The right-hand column is a nested call with two plots
                    labels = c("B", "C"),
                    nrow = ...), # arrange the right-hand column as two rows
          ncol = ..., labels = "A") # Arrange the outer grid as two columns
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

5.1.3 Small changes can be made with align and font()

If y-axis lines or x-axis lines are not aligned, this can be fixed with a call to align = "v" or align="h". Note that this will align the edges of the plot object, and not the panels that represent data alone. For the mismatch between panels B and C, you can see the titles line up but the backgrounds are off and this is due to the unit differences between each plot.

To make sure all axis titles are the same size, we can use font() to specify which text we want changed and the size we want to change it to. I am also going to make the legend title size the same.

Let’s look at the font() function, which is actually part of the ggpubr package. You’ll see that we can treat it much like adding a layer to our plots as we use the + operator. It acts like a wrapper to directly alter the ggplot object through underlying calls to the theme layer. Although limited, there are a number of elements that it can affect, including fonts for:

  • The individual plot titles: “title”

  • Axis and legend titles: “axis.title”, “x.title”, “y.title”, “legend.title”

  • Axis labels: “xy.text” or “axis.text”

More about the font() function: There are a few more basic elements you can alter through this function and you can find out more at the rdrr.io website.

Let’s try out the font() function now and save the result into a new variable multiplot. You’ll notice it’s still not quite perfect but better in many places.

# Alter the fonts of our layout
# set all axis and legend fonts to size 9
multiplot <-
ggarrange(beeswarmPlot + 
            ... +
            ...,        # Alter boxplot fonts
          
          ggarrange(densityPlot + 
                    font("axis.title", size=9) +   # Alter KDE fonts
                    font("legend.title", size=9), 
                    
                    scatterPlot + 
                    font("axis.title", size=9) +
                    font("legend.title", size=9),    # Alter scatterplot fonts
                    
                    labels = c("B", "C"),
                    # Try to align the vertical axis of the histogram and scatterplot
                    nrow = 2, align = "v"),        
           ncol = 2, labels = "A")
## Error in ggarrange(beeswarmPlot + ... + ..., ggarrange(densityPlot + font("axis.title", : '...' used in an incorrect context
# View the updated plot
multiplot
## Error in eval(expr, envir, enclos): object 'multiplot' not found

5.1.4 Save your multipanel plots with ggsave()

The ggarrange objects, while structurally different from ggplot objects, inherit much of their information and behaviours from the ggplot class. Therefore, you can use other ggplot functions like ggsave() to write your plots to file. The calls follow the same format as previous examples we’ve used so let’s give it a try.

# Confirm the object type of our multiplot 
class(multiplot)
## Error in eval(expr, envir, enclos): object 'multiplot' not found
# Save it to a JPEG file for using in our presentations
ggsave(plot = ..., file="data/multiplot.jpg", width = 200, height = 110, units = "mm")
## Error in eval(expr, envir, enclos): '...' used in an incorrect context

Comprehension Question 5.0.0: Make a multi-panel combined figure using our three plots densityPlot, scatterPlot, and beeswarmPlot. This time, put the densityPlot across the top row, and beneath that, combine the scatterPlot and beeswarmPlot across the bottom row. Make sure the legend and axis titles are the same size. Change the legend text for the beeswarm/boxplot to be smaller than the legend title.

# comprehension answer code 5.0.0

# Let's arrange a new set of panels
ggarrange(...)

5.3.0 Upset plots summarize your data

5.3.2 Working with ComplexUpset to visualize overlapping datasets

Let’s see how UpSet plots work practically. Let’s begin by importing our metadata from data/infection_meta.csv to help us determine the overlap in microsporidia strains tested across the various C. elegans worm strains used. Basically we can identify the overlap of strains between microsporidia.

# Import the infection metadata
infection_meta.df <- read_csv("...")
## Error: '...' does not exist in current working directory ('C:/Users/mokca/Dropbox/!CAGEF/Course_Materials/Introduction_to_R/2024.09_Intro_to_R/lecture_04_ggplot2').
#Take a look at the data structure
str(infection_meta.df, give.attr = FALSE)
## Error in str(infection_meta.df, give.attr = FALSE): object 'infection_meta.df' not found

5.3.3 Format your data for ComplexUpset

The data we have represents 276 experimental conditions each noting which worm strains were tested against various microsporidia strains. We’ll want to simplify all this information using our standard group_by() and summarise() paradigm. For simplicity, we’ll capture the number of instances of each worm strain/spore strain combination in our experiments.

The format we want to generate is to have our categories as columns (ie spores), and our observations as rows (ie worm strains). To accomplish that, we’ll have to further pivot_wider() our summarised data. Let’s save the result to a new variable infection_combinations.df.

# save our results to this variable
infection_combinations.df <-
  # Pass along the metadata
  infection_meta.df %>% 
  # Group by worm strain and spore strain
  group_by(Worm_strain, `Spore Strain`) %>% 
  # Count occurences within each group
  summarise(nTotal = n()) %>% 
  # Ungroup the data
  ungroup() %>%
  # Pivot the summary table to move the spore strain names as their own columns
  pivot_wider(names_from = ..., values_from = ..., values_fill = ...)
## Error in infection_meta.df %>% group_by(Worm_strain, `Spore Strain`) %>% : '...' used in an incorrect context
# Take a peek at the result
head(infection_combinations.df)
## Error in head(infection_combinations.df): object 'infection_combinations.df' not found
str(infection_combinations.df, give.attr = FALSE)
## Error in str(infection_combinations.df, give.attr = FALSE): object 'infection_combinations.df' not found

5.3.3.1 mutate() values in multiple columns using the across() helper

Our resulting tibble now has 21 rows (worm strains) and 11 columns (spore strains). Before we continue we want to convert all of the values representing spore strains to either 0 or 1. Any entries with a value of 1 or more (present) can be converted just to 1, and 0 (not present) will remain 0. There are a few ways we could do this but we’ll do a simple mutate and use the ~ syntax again to define a quick function.

# Replace our combo information with the new values of either 0 or 1
infection_combinations.df <-
  # Pass the combinations tibble
  infection_combinations.df %>% 
  # Mutate columns 2-11
  mutate(across(.cols = ..., 
                .fns = ...)) 
## Error in mutate(., across(.cols = ..., .fns = ...)): object 'infection_combinations.df' not found
                # Define our function by casting a conditional result to numeric
                # You could also cast ~as.numeric(as.logical(.x)) instead

head(infection_combinations.df)
## Error in head(infection_combinations.df): object 'infection_combinations.df' not found

5.3.4 Use the upset() function to generate an UpSet plot

Now that we’ve properly formatted our table infection_combinations.df, it has 21 rows (worm strains) by 11 columns (10 spore strains we are investigating)

To use the upset() plotting function, we enter our data set, the number of sets we are inputting, if we want to order the results (in this case by frequency), and how many intersections we want to show. Here, I will show 15 intersections - we know the remaining intersections would be zero since this is ordered by frequency.

Watch out! Remember we said that the tibble and data frame were interchangeable for most cases? When we venture outside the tidyverse we may not be afforded the same courtesy. In the case of the ComplexUpset package, it prefers to work with data.frames instead of tibble objects.

# Load the UpSetR package
library(ComplexUpset)

      # Our dataset  
upset(...,                
      # Name the columns we want to analyse
      intersect = colnames(infection_combinations.df)...,   
      # Set the label below the intersection matrix
      name = "Infection Condition",                            
      # Make the set size width a little smaller
      width_ratio = 0.1,                                       
      # Require a minimum of 1 instance to show an intersection
      min_size = 1,   
      # Set the max number of intersections we want to plot
      n_intersections = ...,                                    
      # Set the plot text size to be 20
      themes = upset_default_themes(text = element_text(size = 20))  
     )  

# This UpSet plot shows testing occurrence between worm strains and spore strains
## Error: <text>:7:54: unexpected symbol
## 6:       # Name the columns we want to analyse
## 7:       intersect = colnames(infection_combinations.df)...
##                                                         ^

5.3.5 Understanding our Upset plot

Our plot can be broken into 3 sections.

  1. The left-hand barplot denotes the number of observations in each set/category.

  2. The bottom plot graphically represents the different combinations of each category up to nintersects.

  3. The upper barplot displays the number of occurrences for the combination displayed in the bottom plot.

There are a few things we can quickly point out about our data:

  • From our result, our greatest intersection size is 9 worm strains tested against the LUAm1 spore strain. This means that 9 of our 21 worm strains have only been tested against the LUAm1 spore strain.

  • At the middle point, we can see that a single strain, is tested against all 10 of the available spore strains in our metadata. This is likely the N2 strain since it is our lab reference control.

  • Looking at the numbers above the bar graphs, we see that this sums to 21 which makes sense since there are only 21 worm strains in our data set.

5.4.0 But wait, there’s more!

While we have just scratched the surface of ggplot, as mentioned earlier in lecture there are many additional visualization packages that can work with more specific types of data. In some cases, these packages add functionality to the ggplot package itself!

5.4.2 Network diagrams

visNetwork (based on igraph): https://datastorm-open.github.io/visNetwork/edges.html

6.0.0 Class summary

That’s the end for our fourth class on R! We took a break from data wrangling this week to focus on the basics of data visualization including:

  1. Understanding the grammar of graphics philosophy.
  2. Producing basic plots: scatterplot, barplots, and boxplots.
  3. Customizing plot elements and themes
  4. Saving your plots to file
  5. Arranging multiple plots into a single canvas.
  6. Packages outside of ggplot.

6.1.0 Submit your completed skeleton notebook (2% of final grade)

At the end of this lecture a Quercus assignment portal will be available to submit a RMD version of your completed skeletons from today (including the comprehension question answers!). These will be due one week later, before the next lecture. Each lecture skeleton is worth 2% of your final grade but a bonus 0.5% will also be awarded for submissions made within 24 hours from the end of lecture (ie 1600 hours the following day). To save your notebook:

  1. From the RStudio Notebook in the lower right pane (Files tab), select the skeleton file checkbox (left-hand side of the file name)
  2. Under the More button drop down, select the Export button and save to your hard drive.
  3. Upload your RMD file to the Quercus skeleton portal.

6.2.0 Post-lecture assessment (6% of final grade)

Soon after the end of each lecture, a homework assignment will be available for you in DataCamp. Your assignment is to complete all chapters from the Introduction to Data Visualization with ggplot2 course which has a total of 4 chapters and 4,300 points. This is a pass-fail assignment, and in order to pass you need to achieve a least 3,225 points (75%) of the total possible points. Note that when you take hints from the DataCamp chapter, it will reduce your total earned points for that chapter.

In order to properly assess your progress on DataCamp, at the end of each chapter, please print a PDF of the summary. You can do so by following these steps:

  1. Navigate to the Learn section along the top menu bar of DataCamp. This will bring you to the various courses you have been assigned under My Assignments.
  2. Click on your completed assignment and expand each chapter of the course by clicking on the VIEW CHAPTER DETAILS link. Do this for all sections on the page!
  3. Carefully highlight/select the page starting with the course title (ie Introduction to R) and going to the end of the last section. Avoid using ctrl + A to highlight all of the visible text.
  4. Print the page from your browser menu and save as a single PDF. In the options, be sure to print “selection” or you may not be able to print the full page. It should print out something like what follows, except with more chapter info.

You may need to take several screenshots if you cannot print it all in a single try. Submit the file(s) or a combined PDF for the homework to the assignment section of Quercus. By submitting your scores for each section, and chapter, we can keep track of your progress, identify knowledge gaps, and produce a standardized way for you to check on your assignment “grades” throughout the course.

You will have until 12:59 hours on Wednesday, October 2nd to submit your assignment (right before the next lecture).

6.3.0 Acknowledgements

Revision 1.0.0: materials prepared in R Markdown by Oscar Montoya, M.Sc. Bioinformatician, Education and Outreach, CAGEF.

Revision 1.1.0: edited and prepared for CSB1020H F LEC0142, 09-2021 by Calvin Mok, Ph.D. Bioinformatician, Education and Outreach, CAGEF.

Revision 1.1.1: edited and prepared for CSB1020H F LEC0142, 09-2022 by Calvin Mok, Ph.D. Bioinformatician, Education and Outreach, CAGEF.

Revision 1.1.2: edited and prepared for CSB1020H F LEC0142, 09-2023 by Calvin Mok, Ph.D. Bioinformatician, Education and Outreach, CAGEF.

Revision 1.2.0: edited and prepared for CSB1020H F LEC0142, 09-2024 by Calvin Mok, Ph.D. Bioinformatician, Education and Outreach, CAGEF.

6.4.0 Your DataCamp academic subscription

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